GM-36599-A is used to turn the side bearing adjuster nut(s) during set-up of the 8.25" and 9.25" ring gear front drive axles. The adjuster design was changed to allow more precise adjustment, and previously essential GM-36599 will no longer fit the current production or service adjuster. GM-36599-A will fully engage the teeth on the adjuster, and has a 3/8" square drive to allow the technician to properly adjust the side bearings on the front drive axle. GM-36599-A fits both left and right side adjusters on 8.25" ring gear axles, and the right side bearing adjuster on the 9.25" ring gear axles.