Guides
21 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
How the three-digit AS568 dash number encodes an O-ring's cross-section and inside diameter, what the 2-XXX and mil-spec prefixes add, and how to find yours.
Metric O-Ring Sizes: How to Read and Convert Them
What a metric O-ring callout means, how ISO 3601, DIN 3771, JIS B 2401 and BS sizes differ, which cords interchange with AS568, and how close the nearest metric size is.
O-Ring Chemical Compatibility Guide
A first-pass compatibility screen for the common O-ring materials, how to read a rating, what changes it, and the eight compatibility traps.
What Causes O-Ring Compression Set?
What compression set is and how it is measured (ASTM D395, the D2000 suffix B), the four causes, how to tell it from other failures at teardown, and how the gland is designed to survive it.
Which O-Ring Durometer (Shore A Hardness) to Pick
Why 70 Shore A is the default, the defaults by material and application, the published pressure-versus-clearance tables by hardness, and when a backup ring beats a harder ring.
O-Ring Groove Design: Gland Dimensions by Cross-Section
Groove width, depth, squeeze and fill for every AS568 family across static face, static radial and dynamic glands, from the published manufacturer guidelines, with surface finish, dovetail and backup-ring rules.
How Much Squeeze Should an O-Ring Have?
Published squeeze bands by seal type and AS568 cross-section, the 0.007 in floor, and what temperature, swell and stretch do to the number.
O-Ring Temperature Ranges by Material
The Parker handbook ranges for every material, what happens at each end, how temperature changes the gland, and why a temperature in a specification title is not an operating limit.
FFKM Brands and Grades Cross-Reference
Seven companies sell perfluoroelastomer (FFKM) O-rings under seven brand names, 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 the brands, their owners and the maker figures on file 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.
Material
One guide per compound family we supply, with the Parker ranges on file; 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
The everyday oil-service seal against its high-temperature upgrade: temperature, fuel chemistry, ozone and budget decide, with HNBR as the middle option.
EPDM vs Fluorocarbon (FKM) O-Rings
Water-side versus oil-side: the two materials divide cleanly on what the seal touches, and the one rule about oil that catches people.
FFKM vs Fluorocarbon (FKM) O-Rings
Perfluoroelastomer against standard fluorocarbon: near-universal chemical resistance at a serious cost step, and the cases where FKM is the right answer anyway.
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.
Specification
The aerospace, quality and food-contact documents a print or a purchase order names, and what they mean for the part.
AMS7276 O-Rings
AMS7276 fluorocarbon O-rings for aircraft fuel and engine oil systems, called out by AS3209, AS3208 and AS83248/1: the document, the part numbers, the material and the RFQ.
AMS7280 O-Rings
AMS7280 fluorocarbon O-rings called out by AS3084 and AS3085: the document, how it relates to AMS7276 and the M83248 family, and which one to quote.
FDA and Food-Grade O-Rings: What Qualifies
What FDA compliant means for an O-ring compound (21 CFR 177.2600), how NSF, USP Class VI, ISO 10993 and 3-A differ, which materials are offered, and what the RFQ must state.
M83248 O-Rings
The M83248/1 and /2 fluorocarbon O-ring family: what the part number means, the cancelled MIL-R-83248 lineage and its SAE successors, and what an RFQ needs to state.
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.
O-Ring Shelf Life and SAE ARP5316
O-ring shelf life is counted from the cure date the manufacturer stamps on the lot, and the reference the seal manufacturers cite for storing elastomer seals is SAE ARP5316, Storage of Elastomer Seals and Seal Assemblies Which Include an Elastomer Element Prior to Hardware Assembly (revision E, 2018); SAE has since reissued the same document as the aerospace standard AS5316 (current, reaffirmed 2022-11-17) and marks ARP5316 as being cancelled and replaced by it. Older prints and purchase orders still cite MIL-HDBK-695. This page explains what the document covers, compiles the shelf-life bands the seal manufacturers publish for each compound family, and says what to write on a purchase order.
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 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.
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.
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