AS568-345 O-ring: 3.975 in ID x 0.210 in cross-section

AS568-345 is the dash number the military and SAE part standards below use for this same nominal size. The document sets the compound; the dash sets the nominal dimensions. When the print calls it out as a part number, such as M83248/1-345, follow that number to its own page for the document status and both units.

Document statuses are read from DLA ASSIST and SAE Mobilus (read 2026-09-24 and 2026-09-25, with SAE's current-revision records read 2026-09-27). This table carries no durometer; the document sets it.

To quote it, send the designator exactly as the print reads, with its revision and any suffix letter. Parts are supplied against the document named and quoted in the compound the print calls out. MS28774-345 is the single-turn scarf-cut PTFE back-up ring on this dash and MS27595-345 the continuous one; the Parker O-Ring Handbook's back-up ring cross reference (ORD 5700A/US, section 6, pages 6-8 and 6-9, read 2026-09-25) lists both under its SAE AS8791 PTFE heading, and the double-turn MS28782 rings run their own numbering, so send that number as printed.

• The MS28775 Revision E sheet (1984-03-23), the DoD drawing behind the MS28775 part numbers, lists -345 at the AS568-345 nominal size, and it holds the inside-diameter tolerance tighter than AS568 above 0.500 in ID. DoD canceled the drawing on 2000-09-29, and SAE-AS28775 superseded it with the same part numbers (DLA ASSIST ident 41724, read 2026-10-04). Your drawing governs.
• DLA ASSIST records MIL-P-83461/1 as canceled on 2003-10-01 and superseded by SAE-AMS-P-83461/1, and DoD's adoption of SAE-AMS-P-83461/1 as withdrawn on 2010-01-20, superseded by SAE-AS83461/1 (DLA ASSIST idents 33814, read 2026-09-24, and 213939, read 2026-09-25).
• DoD cancelled MIL-R-83248/1, the slash sheet behind the M83248/1 part numbers, on 2008-07-24 and pointed future purchases to SAE AS3209, with the boss sizes (M83248/1-901 to -932) to SAE AS3208; SAE later issued AS83248/1, O-ring molded from AMS7276 material, in December 2014, and DoD adopted it on 2025-11-03 (DLA ASSIST: MIL-R-83248/1A Notice 5, read 2026-09-29, and ident 286630, read 2026-09-25; SAE Mobilus AS83248/1A, read 2026-09-27).
• The records name two SAE documents for MIL-R-83248/2: DLA ASSIST records it as canceled on 2004-01-22 and superseded by SAE-AS3581 and SAE-AMS7259, and AS3581's current revision, AS3581A, was stabilized in May 2020; SAE also issued AS83248/2, O-ring molded from AMS7259 material, in December 2014, and its current revision, AS83248/2A (revised October 2016, reaffirmed November 2021), was adopted by DoD on 2025-11-03 (DLA ASSIST idents 33575 and 286631, SAE Mobilus AS3581A and AS83248/2A, all read 2026-09-28).
• M83485/1 is a low-temperature fluorocarbon, not a fluorosilicone; one manufacturer's aerospace cross-reference (Freudenberg, July 2024, read 2026-09-27) lists it against AMS7287. Both SAE successors DLA ASSIST names are cancelled: it records MIL-R-83485 and its O-ring sheet, MIL-R-83485/1, as canceled on 2002-10-23 and superseded by SAE-AMS-R-83485 and SAE-AMS-R-83485/1 (idents 33839 and 33840, read 2026-09-28), and SAE cancelled AMS-R-83485 in May 2014 (AMSR83485A) and AMS-R-83485/1 in June 2015 (AMSR83485/1A) (SAE Mobilus, read 2026-09-27 and 2026-09-28).
• The M25988 slash sheet carries the class and grade; the base document carries the qualification list. The slash sheets are Active; the base MIL-DTL-25988D was noted inactive for new design on 2025-06-11 and in part superseded by SAE AMS-R-25988, which SAE had cancelled in August 2017 (DoD withdrew its adoption on 2018-01-02) and reissued as revision B in June 2023 (DLA ASSIST, read 2026-09-24 and 2026-09-28; SAE Mobilus, read 2026-09-27).
• The MS29513 Revision C sheet (1966-09-16), the DoD drawing behind the MS29513 part numbers, lists -345 at the AS568-345 nominal size, and it holds the inside-diameter tolerance tighter than AS568 above 0.500 in ID. DoD canceled the drawing on 2001-03-01, and SAE-AS29513 superseded it with the same part numbers (DLA ASSIST ident 41788, read 2026-09-27). Your drawing governs.
• One manufacturer's aerospace cross-reference (Freudenberg, July 2024, read 2026-09-27) lists MS9068 against AMS3304 and holds its parts over 0.500 in ID to a tight tolerance; MS9068's document status is not verified here.
• The MS9386 Revision B sheet (1975-01-17), the DoD drawing behind the AS9386 part numbers, lists -345 at the AS568-345 nominal size, and it holds the inside-diameter tolerance tighter than AS568 above 0.500 in ID. DoD canceled the drawing on 1999-10-15, and SAE-AS9386 superseded it with the same part numbers (DLA ASSIST ident 37861, read 2026-09-27). Your drawing governs.
• Minnesota Rubber and Plastics numbers its Quad-Ring® sizes Q4 plus the AS568 dash (Groove Design: Quad-Ring Brand Seals, the starting-dimensions table); availability by dash follows that table.

Groove dimensions for this cross-section are not tabulated here. SAE AS4716 (static and dynamic) and AS5857 (static) set the glands for AS568 sizes, and ISO 3601-2 sets them for metric hardware; the groove design guide explains squeeze, stretch and gland fill, and your drawing governs.

Nearby sizes in the 3xx series

Nearby sizes from the same Parker ORD 5700 section IX AS568 tables as the dimensions above.