COOPER BUSSMANN ACK-300 Low Voltage Fuse, 300A, ACK, 48VDC, Paper. More details: Low Voltage Fuse, 300 Fuse Amps, Nonindicating, ACK Series, 48VDC Voltage Rating, Time Delay, Dual Element, Body Material Paper, Nonrejection, Body Style Bolt-On, Length 3-3/4 In., Diameter 1-1/8 In., Standards UL Guide JFHR2, File E56412