fast-acting fuses?
 

the instructions that came with my autometer gauges state that for the ignition switch connection:

"use a 4amp, 3 AG fast-acting cartridge fuse (littlefuse #312004 or equivalent"

i picked up some 4 amp fuses, but could not find any "fast-acting" fuses. whats the diff? i'm guessing the fast-acting have a thinner wire in them, but does it really matter which ones i use???????