Drum Gear DGA S1B is a "butt plate" for SnareWorks snare drums.
This butt plate sits on the opposite side of the seiding tensioner on the snare drum. It grips the wire, or nylon strap, from the opposite side of the seiding.
This butt plate is from the Drum Gear mk2 SnareWorks snare drums.
The butt plate also fits Drum Gear's SnareWorks mk1 snare drums - and any other snare drum where the space between the holes is this size.
Space between the screw holes: 61mm.