I think a fuse is a fuse is a fuse like atomarc said. I think that the 3 different sizes is based on "smaller better and times are a changin'". My original question was based on my age. Back in 1995 I had a friend who was a PC board designer for a company that made indutrial use equipment. His company was changing from hand placed component boards to automatic placement. He said that the "size" of the SOME of the hand placed components (mostly resistors & capacitors) were bigger than the automatic components that were available on the "reels". They were having problems with some of these smaller components breaking down after repeated "heating up and cooling down" which were driving their engineers nuts. Needless to say they adapted and hand placed the components that needed to be hand placed. Sorry for rambling.

Always get a 2nd opinion, especially if I am the source of the 1st opinion.