Mini Roto-Grip Locking Rotomatics (505 Series) For Standard Guitars Locks Automatically Quick String Change 18:1 Gear Ratio for Precise Tuning Set of 6-In-Line Black Chrome Finish Fits Most Guitars Without Modifications (Hole size .391 ~25/64) Part #: 505BC6 We carry many other Grover Machine Heads, please check our other listings... Condition: New In Package Rotomatic (505 Series) A smaller version of the regular size ROTO-GRIP lockers for the in line and smaller headstocks or for those who prefer a lighter feel. Grover tuners have been keeping the world's finest guitars in tune for almost a century. Known and trusted as the finest tuners available.