Eaton Bussmann Series Class RK5 fuse, FRS-R, time-delay, dual-element, current limiting fuse, 50 A, non-indicating fuse, interrupting rating of 200 kA at 600 Vac and 20 kA at 250 Vdc
Bussmann Fuse, Semiconductor Fuse, Time Delay Fuse, High Speed Fuse, Class J Fuse, Class T Fuse, Class cc fuse, Class RK1 Fuse, Class RK5 Fuse, Class L Fuse, DC Contactor, Disconnect Switch, Car Fuse, Current Limiting Fuse, HV Fuse, Bussmann Fuse Holder, AC Fuse, DC Fuse
You can ask any Bussmann fuse and fuse cross reference(Littelfuse, Mersen, etc).