Since fuses are selected on the basis of system voltage, fuse blocks are selected to match the voltage rating of the fuse. Class H and Class R fuse blocks are dimensionally the same, but Class R blocks incorporate a rejection feature, which only allows Class R fuses to be inserted. Class H and Class R fuse blocks feature clip designs to maximize electrical contact and minimize heat rise. Reinforcing clips are standard on all Class H fuse blocks rated 100 amp and higher. Note: For reinforcing clips on Class H blocks rated 30-60 amp, add R suffix to connector type.