Fuse Size?

[67C10Step]

So, I was working on straightening out a bit of wiring on my 67 over the weekend and had a mishap. The junction block on the right side fender by the battery has the fusible link from the battery to the junction block, then a 12 gage red wire that runs across the core support to join up with the alternator/voltage regulator, etc. and then there is the 18 gage black wire with a fuse that says it goes to the engine harness connection, or at least that's what is says on my wiring diagram.

Anyone know what size the fuse is? Mine got broken by a dropped tool. From the filament it doesn't look too large. It is not listed on my wiring diagram but I am sure I have something I can splice back in there. My father in law had a Radio Shack back in the 1980's and I got a TON of glass fuses and all sorts of fuse hardware.

Thanks in advance.