Oil dipstick

Aka "Filler plug assembly," this is the black plastic version of the engine oil dipstick/filler plug. Fits all Ural engines.

The most likely reason you need this is that your engine had a metal cap dipstick, someone over-tightened it, and the cap broke when you used a wrench or pliers to loosen it. But hey, the plastic one won't burn your fingers as easily when the engine is hot, so this is an upgrade.