This is a rubber-band case for quite decent, cheap (~$15) china diving compass (link)

For assembly you need four M3x10 screws.

IMPORTANT: screws have to be made from A2 or A4 stainless steel (or another non-magnetic alloy that will not interrupt compass readings)

As the bottom is slightly profiled to be worn on left hand, you need to mirror the parts to be used as a right hand model.