Kuzman's right. They'r eintergrips- used to hold two panels for butt welding together where standard c-clamps and welders' clamps won't work due to obstructions or distance. Once the panels have been tacked together these can be removed and re-used. These leave a small gap that the weld wire fills leaving a neater weld wil less grinding, in theory. An alternative are clecos, for lap welds in similar circumstances....