Grover 143 Series Lightweight Bass Guitar Machines. For the ultimate in weight control, Grover offers the 143 series for Bass Guitar. With a plastic housing and aluminum string post, this lightweight bass key is perfect for the player who is concerned about the overall weight of the instrument. The 20:1 gear ratio provides the finest tuning available. Several configurations and are offered, all with a black plastic bass plate and plated button and post. (Includes: four bushings having an outer diameter of 0.66” and internal M19 x 1.0 threading and four washers). 4 Treble, Set of 4