This assembly is used for the rear release option on a funny car body. The M-25-RB slip over the 1/2" x .058 4130, but are NOT welded. These are welded to the rear support bar at time of installation. The tubing blank lengths are as follows: 18" -- 5/16" x .049, & 20" -- 1/2" x .058. Rear Hinges sold seperately, M-120-1 for 3/8" thick, and M-120-1A for 1/4" thick. M-25-1 may be required if this is the first M-25 customer has purchased.