80/20 10 Series 4080 5-HOLE "T" JOINING PLATE by 80/20 Inc. $7.00. 10 Series 4080 5-HOLE "T" JOINING PLATE. 80/20 Inc joining plates, brackets, and pivots can be used for joining 80/20 Inc T-slot profiles or for mounting a variety of 80/20 Inc parts and accessories.