Hi Sebastian,
This is a new genII OPW. The hole is where a cap screw goes with some mounting hardware and a spring to preload worm against the worm gear. To use thew newer genII OPWs you need a drilled and tapped hole in the plate that the OPW is attached to. You will need some hardware to do this, what other bits came with the new OPW? Please show photos of the other hardware.?
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Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
Chip Louie