System, including methods and devices, for bone fixation with a pin and a collar. In exemplary embodiments, the system may comprise a pin configured to be inserted into a bone, and a deformable collar to retain the pin in the bone. The collar may be configured to be operatively disposed on the pin such that the collar extends more than halfway and less than completely around the pin. The pin and the collar may have complementary surface features that discourage sliding of the collar along a long axis of the pin. In some embodiments, the collar may be configured to be operatively disposed on the pin at a plurality of discrete, alternative axial positions along the long axis of the pin. The pin may be cut to a desired length.