Air Vent Screw for Rotax Max Evo Engines. This crankcase vent is a threaded plastic, and allows for excess crankcase pressure and oil to purge from the system during engine operation.
Note that this screw is a 'thumb' type screw, and is intended to purge oil from the gear case of the engine (although it technically threads into the crankcase body).
Each vent screw is M18 x 1.5 thread.