biases the pin tumblers 40 42 inward for mating engagement with a key blade 25 the keyway 24 of the pin tumbler cylinder plug 20 extends radially inward from the outer surface of the pin tumbler cylinder plug and is aligned in the same plane as the pin tumbler cylinder bores 22 the key blade 25 is received in the keyway 24 for axial movement toward and away from the fully inserted locking position the key 26 comprises an edge portion 27 having a bitted surface 27 a which cooperate with the pin tumblers 40 42 in the conventional manner thus when the proper bitted key blade 25 is inserted into the keyway 24 the pin tumblers held in the cylinder plug terminate at the interface 29 of the shell and cylinder plug creating a shear plane so that the pin tumblers do not block rotation of the cylinder plug grooves 46 extend over the key sidewalls over its entire inserted length wherein the grooves conformingly engage aligned sidewalls 48 of the keyway 24 to guide entry of the key blade into the keyway the pin tumbler cylinder plug 20 further comprises one or more chambers 28 for housing a locking member 50 preferably the locking member is a ball bearing more preferably the locking member includes at least two ball bearings the locking member may also comprise a cylindrical shape preferably having opposed spherically shaped ends not shown the locking member may also comprise a pin having opposed spherically shaped ends however ball bearings have an advantage over other shaped locking members in that the ball bearings provide significantly less friction wear and do not require a.