This kit includes (3) steel brackets to make your own portable shooting bench. Brackets are made for 1.5" threaded pipe. Simply attach them to your bench of your own construction, add threaded pipe legs with caps installed, and you have a very sturdy shooting bench. Portable and easily assembled and disassembled.
NOTE: My legs are 32" end to end on my personal bench prototype. Then you add the end cap. This bench has been used by lots of folks, including 6'6" basketball players, and kids on the other end.
I would say 32" threaded on both end 1.5" SCHED40 is the number for a double ply top.