Time delay. Momentary overloads won't blow fuse. Designed to fit matching adapters. 125V AC only. Type S/SL Fuses are designed only to screw into adapters of the same amperage in the fuse holders. This prevents mismatching and the possibility of over-fusing a circuit. The Time Delay Feature of this product prevents temporary power surges from blowing the fuse unnecessarily, as a result of momentary current overloads when appliance motors start up. S & SL (Unique base size for each amperage): Varying base sizes prevent use of wrong amperage. Requires adapters installed in fuse box. Time delay prevents fuses from blowing unnecessarily when momentary voltage spikes occur. Always keep spare fuses on hand. UL Listed.