While I still agree with Red's suggestions, I couldn't help but smile at irony in a glue-up I was doing this afternoon. About 15" x 47" using the pipe clamps. This is a dry fit-up to get the clamps in the right positions. Since this a mortise and tenon frame, the clamp's moveable jaw needs to be up pretty far because when the glue is applied and the frame is set in the clamps, I want plenty of room left on the screws to push things together. Too much foolaround moving the clamp's back jaws will allow the glue to set up where you don't want it to.24" pipes are too short in my opinion unless you do a lot of not wide glue ups.. I would do 36" and bigger. Remember with a 24" clamp you don't have 24" of clamping area.