O-ring kit
Most people picture an O-ring kit as a plastic case with compartments and a few hundred rings. You won't find a ready-made case like that in our catalogue — you assemble the kit yourself from over 6,000 items in the range. Below: what a kit worth having contains, who it pays off for, and when single pieces are the better buy.
An off-the-shelf case mixes dozens of sizes in a single material — almost always NBR. That covers everyday repairs on mineral oil, but the moment you seal glycol brake fluid, steam or hot oil, the whole case is useless: per our material reference NBR works from -30 to +100 °C and is attacked by the glycol-ether brake fluids DOT 3 and DOT 4 (silicone DOT 5 is the exception — NBR handles that one, but glycol fluids call for EPDM).
The second problem is dimensional. A case usually holds a single series — either inch AS568 or metric. If your workshop runs machines from both worlds, half the compartments stay untouched. So it pays to work the other way round: find out which sizes and materials you actually replace on your machines and order only those, in quantities that match your consumption.
- Over 6,000 items across the metric series and inch AS568 — including sizes a universal case never carries.
- Five materials (NBR, FKM, EPDM, VMQ silicone, PU) with service ranges from -60 to +200 °C depending on the type you pick.
- You set the quantity per size — from a single spare ring to a repeatable service set.
What an O-ring kit contains
Every kit rests on three parameters: the size series, the material and the hardness. A size is two numbers — inside diameter d1 and cross-section thickness d2, in millimetres. The series differ precisely in cross-section: the inch AS568 standard uses 1.78 · 2.62 · 3.53 · 5.33 and 6.99 mm, while metric ISO 3601 runs series A to E with 1.80 · 2.65 · 3.55 · 5.30 and 7.00 mm.
The third parameter is hardness on the Shore A scale. Softer compounds follow surface irregularities better, harder ones resist extrusion into the gap at high pressure; 70 ShA is the most common compromise. Hardness is listed with every size in the catalogue, so you can standardise a kit on one value or deliberately split it.
A workshop kit that actually gets used is usually built on one or two cross-sections and covers a continuous run of inside diameters. Size lists by series — AS568, ISO 3601 and JIS B 2401 — are in the Sizes and standards section, and every row links straight to the matching ring.
Who a kit pays off for
- Maintenance and service workshop
- If you service the same machine park over and over, sizes repeat and downtime costs more than a shelf of rings. Start from the service manuals, add the sizes you genuinely replaced over the past year, and keep a few pieces of each. You can send the list into a quote request and have it to hand for the next order.
- A one-off repair
- For a single repair a kit is pointless. Measure the damaged ring — the method is in the How to measure a ring tool — check the material against the medium, and buy just that one size in the quantity you need. It works out cheaper than a case you take one ring out of.
How to build your kit
Four decisions, after which all that's left is entering quantities.
1. Pick the size series
First establish whether your machines use metric sizes to ISO 3601 (DIN 3771 uses the same numbering), inch AS568, or Japanese JIS B 2401. If you're holding a dash number such as AS568-214, the size converter shows you the metric equivalent.
2. Pick the cross-sections you actually use
Cross-section drives groove depth and width, so a single machine usually repeats just two or three of them. A kit built on two cross-sections and a wide span of inside diameters covers more real repairs than a case holding a few pieces from every series.
3. Match the material to medium and temperature
NBR covers mineral oils, hydraulics and pneumatics up to +100 °C. For hot oil, fuels and aggressive chemistry reach for FKM (-20 to +200 °C); for water, steam and brake fluids use EPDM (-40 to +130 °C); for food contact, VMQ silicone. Check resistance to your specific medium in the chemical resistance table.
4. Set the quantities
For parts you replace regularly it pays to keep several pieces per size; for rare sizes one spare is enough. You enter quantities per size, so a kit doesn't need the same count in every compartment.
What a kit does not cover
A kit solves repeating sizes, not exceptions. Before you order one it helps to know what there's no point looking for in it.
- Sizes outside the standard series — if a ring matches no standard, search it directly by d1 and d2 in the catalogue.
- Other sealing elements — an O-ring kit does not replace rotary shaft seals or flat gaskets; we keep a separate technical reference for shaft seals.
- Fitting aids — cleaners, assembly grease, a caliper or picks live in the Accessories section, not in a ring kit.
- A badly designed or damaged groove — no ring fixes that; recalculate the groove to ISO 3601-2 in the groove calculator.
If a ring failed early, look at the cause first. Cracking, swelling or extrusion into the gap point at the material or the groove — not at how many pieces the kit held. The seal failure diagnosis tool exists for exactly that.