Mechanically engineered to the most precise standards of excellence, with the classic look of vintage styling, Grover?s Vintage 533 locking series come with a ?thumb screw? mechanism, which locks the string into place. Insert the string through the post hole, wrap around once, then lock by tightening with the thumb screw. Worm and gear are cut to mesh perfectly, thereby eliminating backlash and slippage. The housings are self-lubricating for a lifetime of trouble-free service. 15:1 gear ratio.533NK: Nickel for 6 string with safety post with keystone button, 3 Treble and 3 Bass, Set of 6.