This is a pack of four optional Yokomo BD9 Shock Pistons. These pistons feature six holes, 1.1mm in diameter each. This is a piston for the High Big Bore Short Shock for their BD9 1/10 scale touring car platform. The piston has 6 holes, two more than the standard pistons. This allows small vibrations to be better absorbed by the shock package, giving more traction. Along with the increase in number of holes, the piston has a larger outer diameter too, increasing the pressure on the oil during cornering, helping to prevent the rear of the car losing grip in high speed turns.

The diameter of the holes is the same as the standard four-hole piston (1.1mm), so with the increased number of holes as well as the increased piston diameter, you should be ready to test different hardness shock oils when changing pistons. As a recommended starting point, you should try shock oil that is 5-10 cst harder than you use with the standard pistons.