This is the cylinder lock screw for the UMS 7-77cc engine, the seven-cylinder 77cc four-stroke radial from UMS.
The part itself is the screws that lock the cylinder to the crankcase.
Why it is replaced: a security-critical fastener — a loose cylinder screw allows the barrel to move and destroys the base joint. Supplied as a pack of 10, which is how these small parts are normally bought — you rarely need just one.
Fitting note: Use a torque wrench, not feel, and check them again after the first flights.
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