RAF wartime mechanical bomb fuse (INERT).
This bomb fuse or pistol, never contained any explosive content, it was designed purely as an impact type detonator. Screwed into the nose of a general purpose, medium or high capacity bomb, the fuse would arm itself as it fell towards its target. A spring loaded striker mechanism would then stike the explosive store on impact, exploding the bomb.
This example is a very rare type 55 Mk1. It is similar to the more common type 44 in body shape, but has the anemometer type arming vanes. In an excellent overall condition, it completely dis-assembles (see photos). Stamped P55 Mk1 on one of the vanes. Size 4" long x 8" span.