High dielectric plastic. Use to protect wire within flexible metallic conduit (Greenfield, BX). Insert one bushing at each end of conduit. UL approved. No 75400 fits cable range of 14/2, 14/3, 12/2 no 75401 fits cable range of 14/4, 12/3, 6/1, 4/1. No 75402 fits cable range of 12/4, 10/2, 10/3, 2/1. No 75403 fits cable range of 10/4, 8/2, 8/3, 1/1. No 75404 fits cable range of 8/4, 6/2, 6/3, 4/2, 4/3, 6/4.