Littelfuse LFR604003C - LFR LFHThe new Littelfuse Class H and R blocks offer many advantages over previous generations that are noted in the features and benefits section. 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. Features & Benefits - Indication offered on most 250V and 600V versions-DIN Rail releasable for all non-knife blade style fuses-Only one hand is required to release from DIN Rail (lock open lock closed)-Universal mounting holes make for easy replacement-Clip designs maximize electrical contact and minimize heat rise-Reinforcing clips are standard on all Class R fuse blocks