The Quad Coupler 1.5 will clamp from 1.25” OD to 1.5” OD tubing, as well as 1" pipe (1.315" OD.) The Quad Coupler 1.5 is 1.25" thick. The notch on the outside of clamp is 1.26" across the flats and will fit over 1-1/4" square tube, while locking the clamp parallel with the 1-1/4" square tubing. Use the flat face to bolt to a fixture, or to allow the Quad Coupler 1.5 to rotate when fastened to square tubing. The distance from the bottom of the clamped pipe or tube, to the flat or notched connecting surface, is .84". Comes complete with 3/8” x 1.25” socket head cap screw with nylon insert lock nut and Belleville spring washer.