Buying Guide

How to Order Custom O-Rings: The 8 Specifications Your Supplier Actually Needs

2026-10-166 min read

A surprising number of custom O-ring requests arrive as a photo and a line that says ‘we need these, what is the price?’. A good supplier can work from a sample, but every missing detail means an email round-trip — and a wrong guess means rings that do not seal. These are the eight pieces of information that let us quote a custom order in one pass and produce it correctly the first time.

The 8 Specifications to Include in Your RFQ

#	Specification	What to state
1	Application & motion	Where the ring goes and whether it is static, reciprocating or rotating. Motion changes both compound and groove rules.
2	Media	List every fluid it contacts — oil, fuel, additives, and even cleaning/washdown chemicals, which are the most commonly overlooked.
3	Temperature & pressure	Normal range plus peaks (startup, sterilization, process spikes), and whether gas service involves rapid decompression.
4	Dimensions	ID × CS (preferred), or ID/OD, or the hardware dimensions: bore, rod/gland and groove. State mm or inch.
5	Standard or special	AS568 dash, ISO metric size, JIS size, or fully custom. For one-off or very large rings, note whether O-ring cord is an acceptable alternative.
6	Material, grade & hardness	e.g. NBR 70 Shore A, FKM 75 Shore A, FDA silicone 60 Shore A. 70A is the default if you are unsure.
7	Approvals & color	FDA, NSF, WRAS/KTW, UL, or customer-specific requirements; color if the ring is used for identification.
8	Quantity, packaging & timing	Order quantity and expected annual volume, kit/box packaging, required inspection reports (PPAP, CoC, material certs), and delivery date.

What a Good One-Line Spec Looks Like

AS568 -214, NBR 70 Shore A, black, static hydraulic fitting,
mineral oil ISO VG46, -20 to +100°C, max 250 bar,
5,000 pcs, CoC + material certificate, delivery 4 weeks

That single line contains everything needed to quote geometry, compound, quality documentation and logistics. A drawing or a physical sample is even better: a sample lets us measure cross-section, gauge hardness, identify the polymer by lab analysis, and reverse-engineer an exact replacement when no documentation exists.

Three Things Buyers Often Forget

Tolerance expectations. Standard AS568/ISO tolerances cover most industrial work; unusually tight ID or flash tolerances require extra tooling or secondary trimming and should be stated up front.
Tooling for custom sizes. A non-standard ID or cross-section needs a mold. Tooling is a one-time cost with a typical lead time of days, not weeks — ask rather than assuming a custom size is slow.
Annual volume matters. Quoting 500 pieces versus 50,000 changes compression-curing vs. injection molding, packaging, and unit price. Give both sample and projected volumes if you can.

The Process: From RFQ to Delivery

You send the 8 specifications (plus drawing or sample if available).
Our engineering team confirms material, dimensions and tolerances, or proposes the nearest standard size to save tooling cost.
You receive a quotation with tooling cost (if any), unit price, lead time and shipping terms.
On approval, samples are produced and, where requested, sent for your fit and function testing.
Approved samples proceed to serial production with full batch traceability.

If you only remember one thing: the operating conditions travel with the order. A size and a material without media and temperature is half a specification.

Ready to send an RFQ? Our O-ring page lists the standard range, and we provide full OEM/ODM tooling and compounding for custom work — small trial batches to volume production. Send your specifications or sample and our team will come back with pricing and technical confirmation.

Back to All Posts