RS Nylon Insulated Tubular Butt Splice Nylon insulated tubular copper butt splices with a window or sight-hole. These insulated butt splices are Color coded for use with different wire ranges. For suitable crimp tool see stock number 267-3133. Red 0.5 - 1.5 mm2 Blue 1 - 2.6 mm2 Yellow 4.0 - 6.5 mm2