Optional 16, 20 or 24 piece black spline lug bolts 12mm x 1.50 threads lug bolts with socket key. The overall length is 2.73" (69mm) and the shank length is 1.55" (40mm). These lug bolts fit tuner style rims that are designed for ultra thin outer mount where a regular socket won't go in. A six spline installation key is included.