Post clamps can secure an optical mount at any position along the length of an optical post. A C-Clamp is a multifunction post clamp which can be directly attached to a post without having to slide it on from the end of the post, and once installed, provides two mounting points 90° apart for the mounting of components. Also, the C-Clamp can be used as a post collar with the Q-TMS series post holder or can be used to securely post-mount cylindrical optics.