A proximal fitting for a catheter is provided for manipulating a guide wire. The proximal fitting includes a first hub and a second hub that engage one another. A collet having a passage can be inserted into the passage of the first hub while being unable to pass through the passages of the first and second hubs. A first portion of the collet has a convex angular surface and a slot that extends radially from the passage in at least one direction. The convex angular surface of the collet interfaces with a concave angular surface on the first hub or the second hub thereby compressing the passage of the collet in response to the first and second hubs engaging one another.
