The 4" Mega-Square Half Coupler XL is designed to fit 4" square tube. Great for hanging speakers or whatever your application needs from 4" square tube structural members. Easy installation, slide up onto tube, flip the link over, tighten the wing nut. Recessed hex pocket for 1/2" bolts. 1/2:-13tpi x 1.25" grade 8 yellow zinc plated, with 1" Belleville washer and nylock nut provided with clamp. Any length 1/2" hex head bolt may be substituted to fit your application. Utilizing a socket cap screw will allow fastening to loads that have internal threads.