Hillman 3/8 in.-16 x 7/16 in. x 1 in. Stainless Steel Pronged Tee Nut (15-Pack) 4151 - The Home Depot
4 Prong T Nut 5/16"-18 x 5/8" (Tee Nut) Qty: 100 Zinc Plated: Amazon.com: Industrial & Scientific
Amazon.com: NGe M8 x 10mm T-Nuts, 4-Prong Tee Nut Fasteners, Pronged Tee Nut for Wooden Furniture and Climbing Hold, Pack of 100 : Industrial & Scientific