Grover 115 Series Perma Tension 4-string banjo tuning keys. Nickel finish with metal roto style kidney buttons buttons. No slippage, no backlash, no looseness, Heavy knurled bushings with threaded extension, locks permanently into wood. Fits headstock thickness up to 1/2"(13mm). Countersunk button screw regulates tension. Features Grover's lifetime guarantee.