The RCC21 is a nylon insulated butt splice for wire range #12 - #10 AWG. In butt splices, the wires are butted together and crimped at each end of the splice. These splices are color-coded according to wire size. Length 1.26 inches, inner diameter .28 inches and maximum insulation dia .210 inches. The splice is made of high-conductivity electrolytic copper, electro-tin plated. Recommended tool ERG4001.