This swivel clamp is used to connect your 1/4" eyesight post to your 1/4" articulating bracket or mounting post. This is the correct size for our Concentric Ringsights and Removable Articulating Ringsight Bracket. 

Fastened with an Allen bolt, this mount prevents your eyesight from ever moving. The old knuckle screw type sucks in comparison to this. If you happen to still have that type, seriously consider upgrading. It's so worth while.