The 1991 GMC C1500 2wd Pick-up bolt pattern is 5-127 mm. This means there are 5 lugs and the diameter of the circle that the lugs make up measures 127 mm or 5 inches across. To get a close measurement of your 5 lug bolt pattern without a bolt pattern tool you should measure from the center of one lug to the outer edge of the lug furthest from it.
