Shaft assemblies include an elongate shaft having a plurality of closely spaced apart external notches with wall segments having a greater outer diameter than an outer diameter of the notches residing therebetween and at least one self-retaining locking ring that engages one of the notches to axially lock into position on the shaft and provide a pull out force that is between about 100 lbf to about 1000 lbf. The notches can have a width that is between about 0.010 inches to about 0.020 inches, on average, and a depth that is between about 0.001 inches to about 0.010 inches, on average.