5/16-18 Tee Nuts. These are 3-Prong steel T-Nuts with zinc plating and have a straight Barrel.
Used for fastening metal to products made of woods, particle board or plastic. The 3-prong style is used in harder materials to minimize splitting of the mating surface. Available in 5/16", 3/8", 7/16" and 5/8" barrel lengths.