you need to know if it fast or slow blo and the ampere rating. Slo blo tends to have a narrow filament. Fast blo tends to have a thicker filament. this does vary however.
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Just to set things clear:'
Slow Bow fuses have a thick coil of wire inside,sometimes filled with fusible metal.It looks chunky by all means.
Fast blow fuses have a very thin wire inside.
Always ask the manufacturer. If you replace a fast blow fuse with a slow blow one you may get into trouble!
ALL fuses are timed devices. The amount of current they will carry (without blowing) depends on how long the current flows. A common type of fuse will blow in about one second if the current is twice the rating. It can carry even higher current for less time. It will carry its rated current for ever.
A slo-blow fuse will carry current greater than its rating for a longer time. Slo-blow fuses are used where brief current surges well above the steady state current are expected. Typically this is for electric motors, which suck amps at startup, and for electronics power supplies which draw high current until capacitors are charged up.
No thin-wire type fuse is fast enough to protect a transistor from a dead short, although it might avoid secondary failures. There are "Fuses" that can protect transistors, but these are actually transistors themselves (not wire) and they cost as much as or more than the transistors they protect. So they are only used where the protected transistors are difficult or impossible to replace.