Sight Base?

[PAHOGHUNTER]

I found several of these in a box of parts I just purchased at an auction. There are no markings, the base is rounded as if it is designed to mount on a rounded receiver? This is the large one the other 2 are made the same but are smaller.
http://i193.photobucket.com/albums/z17/rldar63/mount.jpg
http://i193.photobucket.com/albums/z17/rldar63/mount2.jpg
http://i193.photobucket.com/albums/z17/rldar63/mount1.jpg

[PAHOGHUNTER]

I believe I found the answer, its for the T/C CONTENDER, RAIL MOUNT.