For Adjusting Idle / Mixture Screws on GM and Chrysler. Heavy-duty flexible shaft for easy access. 55300 "Double D" for GM, '79 through present 55310 1/4" hex for pre-'78 GM 55320 3/32" Hex for '78 -present Chrysler 1.7L - 2.2L engines 55330 4.5mm Hex for '78 and '79 GM 55340 "O" Ring Replacement *Total length- 15 1/2" long *1/4" drive *We do not offer a 3/8" drive