Once you are done assembling the body find the center point of the top of the body and drill a 1/2" hole, 1/2" deep. Now insert the 3/8" tee nut into the hole. Now cut your 3/8" all thread to a length of 2 1/2" long. Next insert it into the hole of the body and then screw on the head to the body. Once your robot is assembled you can now insert the saw blades into the body and the scroll saw blades into the head.