This is the piston pin assembly for the UMS 7-77cc engine, the seven-cylinder 77cc four-stroke radial from UMS.
The part itself is the piston pin assembly with its retaining circlips.
Why it is replaced: supplied as a set so the pin and its retention are renewed together, which is how a pin should be replaced. Supplied as a pack of 4, which is how these small parts are normally bought — you rarely need just one.
Fitting note: Make sure the circlips seat fully in their grooves — a displaced clip will score the bore.
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