Size rejecting plug fuse. No interchangeability prevents installing a higher amp fuse than the circuit was designed for. Has the ability to withstand typical motor starting surges. Use in residential or light-duty motor circuits. These fuses thread into SA adapters. Each kit includes (3) SL-15, (2) SL-20, (1) SL-30 fuses, and a Buss fuse tester. 125V, 15A, 20A, 30A. UL listed.