This is a standard glass cartridge fuse (Part #Fuse 101248). Designed for overcurrent protection in primary power supplies and high-voltage circuits, these compact glass-body fuses safeguard transformers, power lines, and internal chassis circuitry from electrical shorts and current overloads. They were widely utilized in vintage radio receivers, test equipment, and audio electronics produced by manufacturers like Philco, Zenith, RCA Victor, General Electric, and Crosley.