Bussmann T-20 20 Amp Type T Time-Delay Dual-Element Edison Base Plug Fuse, 125V UL Listed, pack of 4 Heavy Duty Time-Delay Plug Fuse used to protect critical motor circuits or motors that cycle on/off frequently An industrial/commercial grade product with exclusive dual element construction. Edison base size. These fuses thread into fuse receptacles The Heavy Duty T fuses are industrial strength products, featuring Bussmann's exclusive Dual-Element construction This spring loaded design provides superior short circuit and overload protection The T fuses have more time-delay than the medium duty fuses in order to better protect industrial motors and critical residential circuits