Fuse size

[Russ T. Fender]

I accidentally blew the fuse on the ammeter in my 30-U because I was too lazy to disconnect the battery before doing some minor electrical work.  No big deal but the fuse looks like it might be the original one and has no markings.  My guess is it's 20 amp but I was hoping someone knows for sure what the correct size should be. I can't find any reference to it in the owners manual.