How to find the right O-Rings AI guide
Written by an AI model from its trained knowledge.
What the AI looks for in O-Rings
- Size by standard
- Specify AS568 dash number (US inch) or metric ID x cross-section; measure ID and cross-section with calipers Common inch and metric sizes are very close, and a wrong cross-section leaks even if the ID looks right.
- Compound matched to fluid
- NBR (Buna-N) for oil, fuel and hydraulics; FKM for heat and chemicals; EPDM for water, steam and glycol brake fluid; silicone for static, food or wide temperature Chemical incompatibility causes swelling or cracking within days or weeks.
- Gland squeeze and stretch
- Typical squeeze roughly 15–30% static, 10–20% dynamic; stretch on installation generally kept under about 5% on the ID Too little squeeze leaks, too much causes compression set or installation damage, and excess stretch thins the cross-section.
- Durometer
- 70 Shore A general purpose; 90 Shore A for high pressure or with clearance gaps that risk extrusion Hardness controls extrusion resistance versus sealing at low pressure.
- Backup rings for pressure
- Add PTFE or hard backup rings in high-pressure dynamic glands or where extrusion gap is large Prevents the O-ring from being nibbled into the clearance gap.
Brands that matter
- Parker: Industry reference for O-ring sizing, compounds and groove design.
- Trelleborg Sealing Solutions: Wide range of standard and specialty compound O-rings.
- Freudenberg: OEM-grade O-rings in a broad compound range.
- Apple Rubber: Known for standard and custom O-ring sizes and compounds.
- Marco Rubber & Plastics: Sells AS568 and metric O-rings in many compounds with clear compound listings.
What to avoid
- Assortment kits that don't state compound or size standard for critical or fuel service
- Silicone O-rings on moving rods or shafts
- EPDM O-rings in petroleum oil or grease
- NBR in automotive glycol brake fluid or prolonged ozone/sunlight exposure
- Rolling or twisting O-rings over sharp threads without a protective sleeve or lubricant
Questions
Can I use a metric O-ring in an AS568 groove?
Only if the cross-section and ID fall within the groove's squeeze and stretch limits; close-but-different sizes are a common cause of leaks.
Should O-rings be lubricated before installation?
Yes, with a lubricant compatible with both the compound and the system fluid, to prevent cuts and twisting during assembly.