By cross-reference, and by nothing else. A filter fits the machines its maker lists. Two filters with identical outside dimensions can have different thread sizes, different sealing diameters and different internal valves — and a photograph of a cylinder shows none of that.
What a cross-reference is
A published list, by the filter maker, of the machines or the original part numbers a filter replaces. It is the specification. A listing that names a machine without publishing the cross-reference has skipped the step that decides whether the part fits.
The two types, which are not a choice
A spin-on filter is a sealed canister that screws onto the engine and is replaced whole. A cartridge filter is an element inside a housing on the engine, replaced with its O-rings. Which one a machine takes is set by the machine, and the manual says which.
Three details that separate a good filter from a cheap one
An anti-drainback valve, which keeps oil in the filter when the engine stops so pressure comes up immediately at the next start. A bypass valve, which lets oil past a blocked element rather than starving the engine. And, on a spin-on, a nut welded to the end — a small feature that turns removal into a job for an ordinary spanner. All three are published where they exist.
The part people forget on cartridge filters
The O-rings. A cartridge element refitted with the old rings leaks, and the rings are cheap and supplied with better kits. Check whether they are in the box before ordering.
Where the interval comes from
The machine’s manual, together with the oil specification. This site reports what a filter publishes about itself; how often your engine wants one is its manufacturer’s statement.
Where this page and the manufacturer’s own paperwork say different things, the paperwork wins. Every weight, shell size, armour level, approval version, viscosity grade, chain pitch, pad reference and torque figure on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And for any oil: the viscosity grade is not the specification. The grade describes flow; the specification printed beside it is what decides whether an oil suits a clutch running in the same oil as the engine. This page reports both as the maker publishes them, and which combination a given engine requires is settled by that machine’s own manual.
Questions riders send in about this
Are original filters better than aftermarket ones?
What can be compared is what each publishes: the cross-reference, the valves, the materials. Aftermarket makers who publish all three can be compared with the original on those lines.
Can I reuse a filter after cleaning it?
A paper element is not cleanable. That is a property of the medium, and it is why they are replaced rather than serviced.
Last reviewed 18 September 2026