The adjustable control arms are stout units. The flex joints have a 21/2-inch diameter body with 11/4-inch diameter threads. The upper arms are made of 13/4-inch diameter, 0.312-wall DOM tubing and the upper control arms are 11/4-inch diameter solid round stock. It is important to have the arms adjusted the same length from left to right; starting at the stock length or within 1/4-inch of stock will get you in the ballpark for a 21/2-inch lift. Make sure to grease the bushings before putting the arms in. Not all control arms have Zerk fittings, and sometimes you can't easily get to those that do.