Ever wonder what the “T” stands for when it comes to fuses? If you answered “Timed” – you are correct! Timed is the correct term for a “slow blow fuse” which are often called “time-delay fuses.” There is also a double “TT” rating which denotes very slow blow fuses. Alternatively, “F” stands for “Fast” or “fast acting fuses” with the “FF” rating for ultra-rapid fuses such as the one shown here. The ultra-rapid fuses operate at higher temperatures so are ideal to provide circuit protection to semiconductor devices. The fast-acting fuses are ideal to protect less sensitive components.