Mersen Class R fuse blocks accommodate all Class R 250 power fuses. A choice of screw, pressure plate, box and special order stud connectors fit a wide range of stranded or solid copper or aluminum wire. Insulators are molded glass-filled polycarbonate (GFPC) with verified dielectric strength in excess of 2500V. 30, 60 and 100A fuse blocks feature a unique adder block which can be snapped onto 1, 2 or 3-pole blocks to form multi-pole segmented blocks of as many poles as desired. All fuse clips are made of high conductivity tin-plated copper, with a choice of spring reinforced clips in 60A. 60 Ampere current rating. #4-14 Wire Range.