O-Rings & Gaskets Technical Resources

Practical guide for choosing the correct o-ring material and size for scuba & service use.

Basics

Term	Meaning	Why it matters
O-Ring	Round elastomer ring used to seal a joint between two parts.	Correct size + material = reliable seal and safety.
Gasket	Flat seal placed between two flat surfaces.	Prevents leaks on face-seals and flanges.
ID / OD / CS	ID = inner diameter, OD = outer diameter, CS = cross-section (thickness).	These 3 values define fit and compression.
Compression	How much the o-ring is squeezed in the groove.	Too little → leak; too much → premature wear.

Best value for most scuba applications. Good oil resistance and strong all-round performance.

Premium chemical & heat resistance. Ideal for demanding use and longer service intervals.

Excellent water/steam and weather resistance. Great for outdoor exposure and certain systems.

Material	Strengths	Typical scuba use	Notes
NBR	Great price/performance, good oil resistance	General seals, fittings, common regulator seals	Reliable everyday choice
FKM (Viton®)	Best chemical + heat resistance	Demanding environments, service kits, long-life seals	Higher cost, premium performance
EPDM	Great water/steam + weather resistance	Specific systems, outdoor exposure	Not ideal for oils/fuels

Important: Always confirm the exact size (ID × CS) before ordering. If unsure, measure the old o-ring with a caliper.

Example	What it means	Client tip
ID 24 mm × CS 2 mm	Inner diameter 24 mm, thickness 2 mm (outer diameter ≈ 28 mm).	When in doubt: match ID first, then CS.

Category	Common area	Typical sizes AS568	Notes
Regulators	Hoses / ports / plugs	010, 011,003	Best to match original spec or manual.
DIN / Yoke	Face seals / valve interface	014, 111, 112	Use quality material + correct lubrication.
Gauges	Spool seals / connectors	013, 014, 006	Replace as a pair when applicable.
Cylinders / Valves	Adapters / caps	015, 020, 019	Check for cuts and flattening.

Component	Seal type	What to watch for
1st stage (ports, plugs)	O-rings	Correct CS; don’t over-tighten.
2nd stage / fittings

Look for cracking, loss of elasticity.
DIN / Yoke interface	O-ring / gasket	Replace at first sign of nicks.
SPG / hoses / spools	O-rings	Replace in pairs where applicable.

Action	How	Why it matters
Clean	Rinse and dry parts before reassembly.	Sand/salt can cut seals and cause leaks.
Lubricate (lightly)	Use approved Silicone grease in a thin film.	Reduces friction and prevents twisting.
Inspect	Check for nicks, flattening, brittleness.	Early replacement avoids failures.
Replace	If damaged, stretched, or deformed.	O-rings are cheap; downtime isn’t.

Question	Answer
Can I use Viton everywhere?	Yes, but it’s not always necessary. Use it when you need higher chemical/heat resistance or longer service life.
How do I measure an o-ring correctly?	Measure the inner diameter (ID) and thickness (CS) with a caliper. Avoid measuring a stretched o-ring.
Why do o-rings fail?	Wrong size, over-compression, poor lubrication, dirt/sand, chemical incompatibility, or age.