Fast/Slow fuse?


I was looking for two kinds of fuses, one slow blow (10A, 250V) and one fast blow (4mA (?), 250V). Went to RadioShack and found that they had fast blow type fuse for 10A/250V and slow blow type for the other.
I just bought them anyway.
What would be the worst possible problem of using fast blow fuse instead of slow blow fuse, and vice versa?
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What I need is 6x30mm 10A 250V slow blow fuses. So far, I found clear glass 8A 250V slow blow fuses and ceramic 10A 250V slow blow fuses.
Are ceramic tubes replaceable with clear glass tubes?

thx
In my experience as long as the rating is the same they are interchangeable, but I do not claim to be a fuse expert.
There's no difference in operation the of a fuse, between glass and ceramic. 10A 3AG(31.8mm X 6.4mm) fuses are made in glass, but they are not common. ie:(http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=3SB%2010-ND)