Electric Locking 3+3 Contemporary Tuning Machine Set 2-Pin Black. The PRL-8311-B0 is a set of Ratio Locking Tuned Machine Heads for an electric guitar that uses three a side tuners. It has a contemporary shaped button, has a two pin casing and is finished in black. *Now includes InvisoMatch Standard Mounting Plates for easy installation. Fits most headstocks.