BWLC46

65-069696

B+W

The B+W Snap-On Lens Cap #310 model has two spring-mounted claws at opposite sides which attach to the inside of the filter or lens threads.  They work on any lens or front-threaded filter with the filter size that matches the size you see here (46mm in this case).  If you have a filter on your lens which has no front threads, you would instead need a B+W #305 model cap.