This is a double rear lens cap for Canon EOS mount lenses from OP/TECH USA.  This cap allows you to store two lenses back-to-back in one slot in your camera bag.  It is made of a super strong and tough plastic and has an o-ring seal to protect against moisture intrusion.  Made 100% in USA.

See my other listings for OP/TECH USA body caps, rear lens caps, and double rear lens caps to fit Nikon F, Canon EOS, and Leica M mounts.