Amazon.com: uxcell M8x1.25mm (Pack of 30) 4 Pronged Tee Nut T-Nut for Table Legs Rock Climbing Wall Woodwork Holds Wood Cabinetry : Industrial & Scientific
T-Nuts for climbing holds
T-Nut 3/8"-16 x 7/16" Stainless Steel, (10 Pack) Choose Size/Quantity, by Bolt Dropper, Pronged Tee Nut. for Wood, Rock Climbing Holds. - Walmart.com