My P938 came with a plastic OBW holster that I never use (wrong hand). This bracket fits inside the belt loop of the holster perfectly to allow it to be mounted to any vertical surface.
It will also work with the holster that came with the P290RS so I'm guessing it will work with most Sig holsters.
Hole size is #4. It worked well with extra screws I had on hand.
Print on its side for no supports, but not as strong at the bolt holes, print right side up with supports for better results.