GM Genuine Parts Manual Transmission Synchro Sleeves are designed, engineered, and tested to rigorous standards, and are backed by General Motors. These sleeves' primary function is to help prevent grinding of gears when your vehicle shifts between them. To do so, they help adjust the rotation of the shafts within the transmission so that the gears remain aligned throughout the shift. The components were designed to help promote smooth shifting and transition between gears and the synchronizer itself consists of a hub, sleeve, springs, and insert keys. GM Genuine Parts are the true OE parts installed during the production of or validated by General Motors for GM vehicles. Some GM Genuine Parts may have formerly appeared as ACDelco GM Original Equipment (OE). WARNING: Cancer and Reproductive Harm