Guides
38 guides written for the engineers and buyers who specify O-rings: AS568 and ISO 3601 sizing, gland design, hardness, compression set, chemical compatibility, shelf life and first-article inspection. The material and specification guides cover the compound families and documents we supply against, and each one names the Parker® O-Ring Handbook or the standard the figures come from.
Reference
Sizing, gland design, hardness and compatibility: the questions behind most RFQs.
AS568 Dash Numbers Explained
An AS568 dash number is a three-digit size code that stands for one nominal inside diameter and one cross-section in the SAE AS568 table, so it is looked up rather than calculated. The first digit names the cross-section family, from 0 for 1/16 in to 4 for 1/4 in, plus 9 for the tube-fitting boss seals, and a higher number within a family means a larger inside diameter: AS568-214 is a 0.139 in cross-section with a 0.984 in inside diameter. The current revision, AS568F, lists 369 sizes.
Metric O-Ring Sizes: How to Read and Convert Them
A metric O-ring is sized by its inside diameter and cross-section in millimeters, written ID x CS, for example 25 x 3.55. Read the cross-section first: 1.78, 2.62, 3.53, 5.33 or 6.99 mm marks an AS568 inch size given in millimeters, while 1.80, 2.65, 3.55, 5.30 or 7.00 mm marks an ISO 3601 metric size. The paired cords overlap closely, and the gland decides whether one can stand in for the other.
O-Ring Chemical Compatibility Guide
Match the O-ring material family to the media first: nitrile and FKM (Viton®) resist petroleum oils and mineral hydraulic fluid, FKM also resists gasoline and diesel, EPDM handles water, steam and glycol brake fluid but never petroleum oil, and FFKM rates well against nearly every media family at a much higher cost. The ratings on this page are general guidance for each family at moderate temperature; temperature, concentration and whether the seal moves change them, and the compound datasheet confirms the choice.
What Causes O-Ring Compression Set?
Compression set is the permanent flattening an O-ring takes after time under squeeze: it comes out of the gland flat-sided instead of round and can no longer push back to seal. The Parker O-Ring Handbook (ORD 5700) lists seven conditions that cause it, among them excess heat, a compound with poor set properties, fluid swell, over-squeeze and incomplete cure, and it sets 0.007 in as the least squeeze to design for. Compounds are compared on ASTM D395 set values taken at the same time and temperature.
Which O-Ring Durometer (Shore A Hardness) to Pick
Most O-rings are specified at 70 Shore A, the default hardness because it balances conforming to the gland surfaces against resisting extrusion. A harder ring is chosen as pressure and clearance rise, and makers' clearance charts, such as Precision Associates' Design Chart 6, give the gap each hardness can bridge at a given pressure. A backup ring is the other route, letting a softer ring hold a higher pressure.
O-Ring Groove Design: How a Gland Is Sized
An O-ring groove is sized from the ring's cross-section, the squeeze the seal type needs and the free volume the ring needs to swell into: Parker's handbook holds gland fill between 60 and 85 percent of the groove volume, with 75 percent as the optimum. Where a drawing names SAE AS4716, AS5857, ISO 3601-2 or MIL-G-5514, that document governs the groove dimensions.
How Much Squeeze Should an O-Ring Have?
A face seal takes the most squeeze: Parker's handbook puts the static maximum for most elastomers at 30 percent and calls that much often beneficial in a face seal. Whatever the percentage, the Parker handbook sets 0.007 in of absolute squeeze as the floor, because below about 0.005 in a ring takes close to 100 percent compression set.
O-Ring Temperature Ranges by Material
O-ring temperature range depends on the material family. On the Parker O-Ring Handbook (ORD 5700) standard ranges, nitrile runs -34 C to 100 C, EPDM -57 C to 150 C, FKM (Viton) -26 C to 204 C, silicone -54 C to 204 C and FFKM -26 C to 320 C, the widest standard span, and special compounds stretch several of these. The compound datasheet sets the final figure, and a temperature printed in a specification title is not an operating limit.
Custom Molded Rubber Part RFQ Checklist
A request for quote on a custom molded rubber part needs eight things: the drawing and 3D model, the parting line and flash limits, the material callout or compound, the hardness and color, the ARPM tolerance class, your annual volume and how you release it, the tooling situation, and the documents you need with the parts. With all eight, the quote is written against your real requirements instead of assumptions. This checklist explains each item and what to send when one is not settled yet.
Cutting conductive silicone gaskets
Yes: conductive silicone and fluorosilicone sheet can be waterjet cut or die cut, and a compounder also offers flash cutting with no tooling [4][5]. The process decides the edge, the tolerance a part can hold, the smallest feature and what can be done with an adhesive backing; it does not change the material, its MIL-DTL-83528 type letter or its lot. Conquest Seal cuts conductive silicone sheet on its own pure-water waterjet, adhesive-backed sheet included, cut through with the release liner on; die-cut parts and parts kiss-cut on a continuous liner go to a cutting partner.
FFKM Brands and Grades Cross-Reference
Each perfluoroelastomer (FFKM) O-ring brand belongs to one company, and every line splits into the same families: a general chemical grade, a high-temperature grade, a steam grade, a high-hardness grade for gas decompression, a low-temperature grade and, for some makers, semiconductor and aerospace grades. This reference puts six brands, their owners and the figures from each maker's own sheet side by side so an "or equal" comparison starts from sheets. Conquest quotes every brand below as a distributor and decides equivalence for none of them.
Hydraulic Rod Seal Installation
Most rod seal failures are made at the bench or by the rod, not by the seal. This guide covers the fit, in the order the parts go into the cylinder head, the failure modes a mechanic can read from the old seal, and what to send so the replacement matches the first time.
O-Ring Part Number Cross-Reference
Yes, an O-ring part number from one maker can be crossed to another supplier, in two halves: the size and the material. The size crosses exactly, because the three-digit dash number is the SAE AS568 size whatever prefix a maker puts in front of it, so a Parker 2-214 is the AS568-214 size. The material does not cross by its code, because a maker's compound number names that maker's own formulation, so the second half of the cross is the specification the print or the maker's sheet names. When the print names only one maker's compound, any substitute is an "or equal" decision that belongs to whoever owns the print. Send us the full callout and we quote the size and the document it resolves to.
EMI gaskets with adhesive backing
Yes. Flat and extruded EMI gaskets can be ordered with a pressure-sensitive adhesive (PSA) backing, laminated by the maker in one of two ways: a non-conductive strip over part of the footprint that leaves bare conductive rubber to touch the flange, or a thin conductive adhesive across the full width [1][6]. Either way the gasket maker's published electrical figures are for material without adhesive, and the adhesive is usually rated to a lower temperature than the silicone it sits on [1][3]. The drawing should say whether adhesive is wanted, whether it must conduct, where it goes and which one.
Kitting and vendor consolidation for seals
Vendor consolidation for seals means buying the O-rings, gaskets and other seals a plant uses from fewer suppliers, starting from one part list. Kitting packs the seals one assembly needs under one kit part number, so the line pulls one kit instead of several bags. Both start with the same clean list: part numbers, revisions, specifications and annual usage. Conquest Seal takes the whole list in one quote request, stocks every AS568 size, and ships releases against a blanket purchase order with each release numbered. This guide covers how buyers run a consolidation, how blanket orders and releases work, what a kit list needs, and what to send for a quote.
Seal types: which seal does which job
Seal types sort by what moves at the joint they close. Static seals, such as gaskets and O-rings, close a joint where nothing moves. Rotating shaft seals work where a shaft turns, and reciprocating seals work on a rod or piston that strokes in and out. Parts that fit no standard type are molded or machined to a drawing.
What is an EMI gasket?
An EMI gasket is an electrically conductive gasket fitted in a seam, door or cover joint so the enclosure stays one continuous conductor across the joint, and radio-frequency energy cannot leak out through the gap or in through it [3]. An enclosure needs one where it must meet an emissions or immunity limit and has a joint that is not welded shut, or flanges that cannot be made flat, stiff and clean enough to conduct on their own [3]. Conquest Seal supplies conductive elastomer gaskets and O-rings from their manufacturers and cuts conductive silicone sheet gaskets to your drawing on its own waterjet.
Material
One guide per compound family we supply, with the ranges Parker publishes; Viton and EPDM live on their material pages.
Comparison
Two families side by side, for the prints that allow either.
Nitrile vs Fluorocarbon (FKM) O-Rings
Buna-N (nitrile) and Viton (FKM) both seal petroleum oils and fuels, so temperature, the chemistry at the edges and cost decide between them. On the Parker O-Ring Handbook (ORD 5700) ranges, standard nitrile runs -34 C to 100 C and standard FKM -26 C to 204 C, and FKM also resists the aromatic fuels, chlorinated solvents, ozone and weather that attack nitrile. Nitrile is the lower-cost industrial default and FKM its upgrade for heat and chemistry, with HNBR between the two at -32 C to 149 C.
EPDM vs Fluorocarbon (FKM) O-Rings
EPDM and Viton (FKM) divide by what the seal touches: EPDM for water, steam, glycol brake fluid and phosphate-ester hydraulic fluid, FKM for petroleum oils, fuels and solvents. EPDM must never see petroleum oil, and standard FKM degrades in steam. On the Parker O-Ring Handbook (ORD 5700) ranges, standard EPDM runs -57 C to 150 C, with steam compounds to 204 C, and standard FKM -26 C to 204 C.
FFKM vs Fluorocarbon (FKM) O-Rings
FFKM is fully fluorinated and Viton (FKM) only partly, which gives FFKM near-universal chemical resistance and a higher ceiling at a large step in cost. On the Parker O-Ring Handbook (ORD 5700) ranges, standard FKM runs -26 C to 204 C and FFKM -26 C to 320 C. FFKM earns its price with ketones, amines, steam, high vacuum or heat above the FKM ceiling; for engine oil, fuel and hydraulic oil at temperature, FKM usually does the job.
Branded vs Generic FFKM: What the Brand Buys You
Kalrez® is one manufacturer's FFKM; Chemraz®, Parofluor® and value-tier lines are the same polymer family. How to read a Kalrez callout, map the grades across brands, and know when an equal is acceptable.
Fluorocarbon (FKM) vs Silicone O-Rings
For dry heat with no oil, the Parker handbook points to silicone; for hot oil, fuel or aggressive chemicals, it points to Viton (FKM). On the Parker O-Ring Handbook (ORD 5700) ranges, standard FKM runs -26 C to 204 C and standard silicone (VMQ) runs -54 C to 204 C, so the top end is a tie and the choice comes down to what the seal touches, how cold it gets and whether the seal moves.
Fluorosilicone (FVMQ) vs FKM O-Rings
The Parker O-Ring Handbook points to fluorosilicone (FVMQ) for a static fuel or oil seal that must stay flexible in deep cold, and to FKM for a seal that runs hotter, meets a wider range of chemicals or moves. On the handbook's figures, fluorosilicone runs from -73 C to 177 C (-99 F to 351 F) and standard FKM from -26 C to 204 C (-15 F to 400 F). Both resist fuels, but fluorosilicone is a silicone at heart and wears poorly, so the handbook keeps it to static seals.
Specification
The aerospace, quality and food-contact documents a print or a purchase order names, and what they mean for the part.
AMS7276 Specification Explained
What AMS7276 is: the SAE fluorocarbon (FKM) material specification behind the AS3209 and AS83248/1 O-rings and the AS3208 seals for aircraft fuel and engine oil systems, its status, hardness and qualification, and what an RFQ states.
AMS7280 O-Rings
AMS7280 is an SAE Aerospace Material Specification for fluorocarbon (FKM, written FPM in the older naming) sealing rings: high-temperature fluid resistant, low compression set, 70 to 80 hardness, and still at revision F from 1992. The part standards AS3084 and AS3085 call it out on AS568 dash sizes, while AMS7276 is the active fluorocarbon document most new drawings use.
FDA and Food-Grade O-Rings: What Qualifies
An FDA compliant O-ring is molded from a compound whose ingredients appear in 21 CFR 177.2600, the FDA regulation for rubber articles in repeated food contact, and that meets its extraction limits; the compound maker self-certifies against the regulation, and the FDA does not approve compounds or parts. NSF/ANSI 51 and 61, USP Class VI, ISO 10993 and 3-A are separate requirements with their own tests and paperwork, so the RFQ names the one the equipment needs.
M83248 Specification: /1 vs /2 and the SAE Successors
An M83248 O-ring is a fluorocarbon (FKM) O-ring called out as M83248/1-XXX (Class 1, 75 Shore A) or M83248/2-XXX (Class 2, 90 Shore A), where the three-digit dash is the AS568 size. MIL-R-83248, the military specification behind the number, was cancelled in 2001 and superseded by SAE documents; the part number is still ordered every day, and the live material specification behind an M83248/1 ring is SAE AMS7276.
AS9102 First Article Inspection
A first article inspection report (FAIR) is the documented evidence that a production part matches every requirement on its drawing and specification, recorded on the three forms SAE AS9102 defines (Aerospace Series, First Article Inspection Requirements; current revision AS9102C, 2023). Buyers ask for one on a new part, after a change, or after a lapse in production. Conquest can provide AS9102 first-article documentation on request, on the form set your purchase order names.
How to Read an ASTM D2000 Callout
An ASTM D2000 line callout names a rubber material in one string on a drawing: the units, a grade, a type letter for resistance to heat aging, a class letter for resistance to oil swell, the hardness, the minimum tensile strength and any added test requirements. SAE J200 is the matching SAE document and is read the same way. This guide explains each part in plain words and works through one example; the test values behind each letter and digit sit in the standard's own tables, which it does not reproduce.
MIL-R-6855 (MIL-PRF-6855): Classes, Grades and Status
MIL-R-6855 is the military specification for synthetic rubber sheet, strip, and molded or extruded shapes, and it is still in force: its current form is MIL-PRF-6855 revision F, which the DLA ASSIST record lists as active, last validated on 1 August 2022. It sorts the rubber into five classes by what it must resist and what it may touch, and into grades 30 to 80 that are the Shore A hardness. A callout such as Class 1, Grade 60 asks for fuel and petroleum oil resistant rubber at 60 Shore A, and the specification lists nitrile as an elastomer that meets Class 1.
Molded Rubber Tolerance Classes A1 to A4
Molded rubber parts are toleranced by class. The Association for Rubber Products Manufacturers (ARPM) defines four classes for the dimensions of a molded part in its Rubber Handbook: A1 high precision, A2 precision, A3 commercial and A4 basic. Each class sets a tolerance band for each size range, and the class you choose drives how the mold is built, how many cavities it can have and how closely the parts are inspected. This guide explains the classes and what moves them; the values are in ARPM's tables, which it does not reproduce.
O-Ring Certificate of Conformance
A certificate of conformance (CoC) for O-rings is the supplier's signed statement that the parts shipped conform to the purchase order and to the specification it names. For mil-spec O-rings you normally need one, because the contract or the purchase order asks for it; no regulation attaches a certificate to the part number itself, and on federal work the clause for a contractor's certificate in place of source inspection is FAR 52.246-15. A certificate of conformance is a statement, not test data, and it is a different document from the manufacturer's own certificate, the batch test report and an AS9102 first article report. At Conquest a certificate of conformance ships with every order and names the part number, the specification, the manufacturer, the lot, the quantity and the manufacturer's cure date.
Lot Traceability for Mil-Spec O-Rings
You check lot traceability on O-rings for a defense contract on paper: the lot number on your supplier's certificate of conformance has to lead back, through the manufacturer's certificate and the cure date, to the company that molded the parts, with every seller in between named. What that paper must contain is set by the clauses and quality requirements in your contract, not by the O-ring's part number. On DLA awards, procurement note C03 has the seller confirm it holds supply chain traceability documentation naming the part number, the manufacturer and its CAGE code, every intermediary and, when available, the lot code. The counterfeit-part clauses buyers often quote, DFARS 252.246-7007 and 252.246-7008, cover electronic parts, not seals; for an O-ring the counterfeit reporting duty comes from FAR 52.246-26 when the contract carries it.
O-Ring Shelf Life and SAE ARP5316
O-ring shelf life is counted from the cure date the manufacturer marks on the lot. The storage document for elastomer seals is SAE ARP5316, Storage of Elastomer Seals and Seal Assemblies Which Include an Elastomer Element Prior to Hardware Assembly; its last issue, revision E, was cancelled in October 2018 and superseded by SAE AS5316. MIL-HDBK-695, the military handbook older prints cite for shelf life, leaves O-rings and other molded seals out of its own tables and refers them to ARP5316. This page states what the two documents say about storage periods by compound family, storage conditions and cure-date counting, and what to write on a purchase order.
What QPL-Listed Means for O-Rings
A QPL-listed O-ring is one whose manufacturer has had that product tested against a military or SAE specification and accepted onto the list the document's qualifying activity keeps; the listing belongs to that manufacturer's product from the listed plant, not to a size, a distributor or a buyer. Only some O-ring documents carry a list. Among the mil-spec families on this site, MIL-PRF-25732 (the MS28775 ring) and MIL-DTL-25988 (the M25988 fluorosilicone rings) carry government lists in the DLA Qualified Products Database, and SAE AMS7276 and AMS7259 (behind the M83248, AS3209 and AS3581 rings) carry non-government lists. You check a government list in the public QPD by specification number, and the manufacturer's certificate for your lot should name the listed source. When a drawing calls out a specification that has a list, the material or the finished molded part has to come from a listed manufacturer; Conquest Seal supplies it on that basis and is not on any list itself.
Onboarding a seal supplier: the documents a buyer needs
Supplier quality and purchasing each open a file when a plant adds a seal, O-ring or gasket supplier. Quality asks for the quality system certificate, a certificate of conformance with each shipment, the manufacturer's material certification and, for a new part, a first article report to SAE AS9102. Purchasing asks for RoHS, REACH and conflict minerals statements, a Form W-9, a certificate of insurance and, before a confidential drawing goes out, a nondisclosure agreement. Most supplier questionnaires also ask about export-controlled data and lot traceability. This guide takes each document in turn: what it answers, what to check, and Conquest Seal's own answer where this site publishes one.
USP Class VI Silicone and O-Rings: What It Means
USP Class VI is the most demanding of the six plastic classes in United States Pharmacopeia chapter 88, which sorts materials by how living tissue reacts to them; a silicone or other elastomer compound meets it when its maker has that exact compound tested and it passes. It is required when the drawing, the purchase order or the device maker's biocompatibility plan names it, most often for medical devices and pharmaceutical processing equipment. The listing belongs to the compound and its maker, so an O-ring meets it only when it is molded from the tested compound and the paperwork names that compound.
Blog
Shorter posts on sealing questions, updates and news from Conquest Seal.
Gasket material by temperature and media
The temperature at the flange and the fluid it holds decide the sheet family before anything else. Elastomer sheets split by media at moderate temperatures; fiber, PTFE, graphite and mica sheets take over where the flange runs hotter or the media attacks rubber. This post lists the published band for each sheet family, what it suits, what it does not, and the callout a print uses.
How to measure an O-ring: ID, OD and cross-section
An O-ring is sized by two numbers: the inside diameter (ID) and the cross-section (CS), which is the thickness of the rubber cord. Measure those two and the outside diameter follows, because OD equals ID plus twice the CS. Match the pair to the AS568 chart and you have a dash number, which is what a print, a purchase order and a quote all use.
Is a Brand-Name Fluoroelastomer the Same as FKM?
Not exactly: Viton is a registered trademark for the FKM polymer families of one maker, Chemours, which took the brand over from DuPont. FKM is the ASTM D1418 designation for the whole class of fluorocarbon elastomers, whichever company made the polymer. Every Viton part is an FKM part; an FKM part is a Viton part only if the polymer came from that maker.
O-ring backup rings: when and how to size them
An O-ring needs a backup ring whenever system pressure, clearance gap, and compound softening combine to push the seal into the extrusion gap between mating parts. Backup rings, also called anti-extrusion rings, sit next to the O-ring in the gland to close that gap without adding pressure capacity themselves. One ring handles one-way pressure; two rings, one on each side, handle alternating pressure. Sizing follows the O-ring's AS568 dash number family, with ring count and placement noted on the print.
O-ring failure modes: how to read a failed seal
A failed O-ring usually shows its cause on its surface. A chewed edge on the low-pressure side is extrusion, a flat-sided oval is compression set, a corkscrew cut is spiral failure, and blisters are gas decompression. Section 10 of the Parker O-Ring Handbook (ORD 5700) groups the modes by appearance; this post puts that reading in the order a technician meets it at the bench.
How to read an AS568 o-ring size chart
An o-ring size chart lists the AS568 dash number for a standard seal along with its inside diameter, cross-section diameter, and the tolerance band each dimension carries. AS568F covers 369 standard sizes, 349 general purpose dash numbers plus 20 boss sizes, maintained in the Parker O-Ring Handbook ORD 5700 size tables. Reading the chart correctly means matching the dash number to the actual print dimensions, not just picking the closest round number.
X-ring vs O-ring: when a four-lobed seal makes sense
An X-ring is an O-ring with a four-lobed cross-section instead of a round one. It fits the same AS568 dash sizes and often the same groove, but it seals on two lines per side, needs less squeeze, and its lobed shape resists the rolling that produces spiral failure in reciprocating service. An O-ring stays the default for static sealing and for the widest choice of compounds and sizes.
Viton is a trademark of The Chemours Company; Kalrez is a trademark of Qnity Electronics; Chemraz is a trademark of Greene Tweed; Parofluor is a trademark of Parker Hannifin Corporation; Parker is a trademark of Parker Hannifin Corporation. No affiliation or endorsement is implied.
Orders are handled under Conquest Seal's AS9100D quality management system, whose certificate scope includes distribution.
Send the part number and we quote it
Part number or drawing, compound if you know it, and the quantity. A Conquest representative reads every request and replies. Quotes answered within one business day. A person answers (714) 632-9830, Pacific business hours.
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