How do I identify the correct scuba O-ring size?

Identify size by measuring the O-ring inside diameter (ID) and cross-section (CS), or by measuring the groove. Then match the nearest AS568 size. Avoid selecting by outside diameter alone.

What is the difference between AS568 ID, CS, and OD?

ID is the inside diameter, CS is the cross-section (thickness), and OD is the outside diameter (OD = ID + 2×CS). AS568 sizes are defined by ID and CS.

Which O-ring material should I choose for scuba use: NBR, Viton FKM, or EPDM?

Match the original manufacturer specification whenever possible. NBR is a common general-purpose option, Viton FKM offers strong chemical/heat resistance, and EPDM is used in specific applications. For oxygen-enriched service, follow manufacturer guidance for materials, cleaning, and lubricants.

Is it OK to replace an O-ring with a similar size?

Not recommended. Small differences in ID or CS can cause leaks or failure. For scuba equipment, use the exact AS568 size and the correct material/hardness specified for your model.

Do I need to lubricate scuba O-rings?

Only if the equipment manual recommends it. Use a compatible lubricant and apply a very thin film. Excess lubricant can attract dirt and compromise sealing.

🤿 Ordering stays open — we’re underwater until September 30, and everything ships on October 1.

Resources

Scuba O-Ring Sizes & Applications (AS568)

A practical reference for the most common AS568 scuba O-ring sizes—with dimensions, typical use cases, and quick product links. If you’re replacing an O-ring, always match size, material, and hardness to your exact model.

AS568 reference dimensions Scuba-focused examples Quick links to buy

Quick rule: O-ring “size” is defined by ID (inside diameter) and CS (cross-section / thickness). Measuring only the outside diameter often leads to mistakes.

Jump to:
How to choose the correct O-ring Materials (NBR / Viton FKM / EPDM) Size table (003, 010–015, 111, 112, 214) FAQ

How to choose the correct scuba O-ring (fast, reliable)

Identify the part (DIN valve, yoke, hose spool, battery cap, port plug, etc.).
Confirm the size (AS568 number if known, or measure groove/old ring).
Pick material based on exposure (air/nitrox, saltwater, oxygen compatibility, chemicals).
Pick hardness (most scuba static seals: ~70A; dynamic/high pressure may differ).
Install correctly: clean groove, no twisting, light compatible lubricant if required.

Safety note: This page is for reference and shopping convenience. Critical life-support equipment should be serviced to manufacturer specs. When in doubt, match the original manufacturer part number and service manual.

Browse Scuba O-Rings O-Ring Kits

Materials used in scuba O-rings

NBR (Nitrile)

Great all-round choice for many scuba seals. Good flexibility and value.

Viton FKM

Excellent chemical and heat resistance. Often preferred for demanding environments.

EPDM

Common for some regulator and valve applications; good resistance in specific use cases.

Tip: For oxygen-enriched service, always follow your equipment manufacturer recommendations (materials, cleaning, lubricants).

Common AS568 scuba O-ring sizes (dimensions + typical uses)

Dimensions below are AS568 reference sizes (ID & CS). Actual best-fit still depends on the groove design and manufacturer specs.

AS568	ID	CS	OD (ID + 2×CS)	Typical scuba applications (examples)	Quick links
-003	1.4	1.5	4.4	HP hose / SPG swivel seal	NBR · EPDM · Viton
-006	2.9	1.78	6.46	Regulator piston & seals	NBR · EPDM
-007	3.68	1.78	7.24	Regulator piston	NBR
-008	4.47	1.78	8.03	Regulator piston ring	NBR · EPDM
-009	5.28	1.78	8.84	Regulator seat seals	NBR
-010	6.07	1.78	9.63	LP hose (2nd stage)	NBR · EPDM · Viton
-011	7.65	1.78	11.21	LP hose 1st-stage 3/8" port	NBR · EPDM · Viton
-012	9.25	1.78	12.81	HP seat seal	NBR · EPDM · Viton
-013	10.82	1.78	14.38	Large port piston seat	NBR · Viton
-014	12.42	1.78	15.98	Yoke (A-clamp) tank valve	NBR · EPDM · Viton
-015	14	1.78	17.56	Tank valve bonnet nut	NBR · EPDM · Viton
-017	17.17	1.78	20.73	Regulator / valve	NBR · EPDM
-019	-	-	-	Regulator / valve	EPDM
-020	21.95	1.78	25.51	Large seal (Sherwood)	NBR
-022	25.12	1.78	28.68	Large seal (Scubapro)	NBR · EPDM
-023	26.7	1.78	30.26	Large seal (Sherwood)	NBR
-024	28.3	1.78	31.86	Large seal (Sherwood/Apeks)	NBR
-025	29.87	1.78	33.43	Large seal (Sherwood)	NBR
-106	4.42	2.62	9.66	2.62 CS series	NBR
-107	5.23	2.62	10.47	Sherwood 6121-129	NBR
-109	7.59	2.62	12.83	2.62 CS series	NBR
-110	9.1	2.62	14.34	2.62 CS series	NBR
-111	10.77	2.62	16.01	DIN reg 1st stage - Apeks	NBR · EPDM · Viton
-112	12.37	2.62	17.61	DIN reg 1st stage - standard	NBR · EPDM · Viton
-116	18.72	2.62	23.96	Tank valve (Genesis)	NBR · Viton
-214	24.9	3.5	31.9	Tank neck / valve seal	NBR
-903	7.65	1.63	10.91	Sherwood (metric)	NBR
-905	10.52	1.83	14.18	Sherwood (metric)	NBR
-906	11.89	1.98	15.85	Sherwood (metric)	NBR

Choosing between materials (fast): If you’re unsure, start by matching the original part (same size + same material). When upgrading, consider the environment (heat/chemicals) and follow manufacturer guidance.

FAQ: O-ring selection (scuba)

How do I identify an O-ring size if I don’t know the AS568 number?

Measure the old O-ring’s ID and CS, or measure the groove. Then match the closest AS568 size from the table.

Why does the same AS568 size exist in different materials?

Size defines geometry. Material defines how the seal behaves (chemical resistance, temperature, compression set, etc.). Choose the material based on your application.

Can I replace an O-ring with “almost the same” size?

It’s risky. A small CS/ID difference can cause leaks or extrusion. For scuba equipment, always match the correct AS568 size and the manufacturer’s spec when available.

Do I need lubricant?

Only if your equipment manual recommends it. Use a compatible lubricant and apply a very thin film—too much can attract debris and compromise sealing.