>Michael, do you see any problems with using the 3/4" rail as a rule? I have all my hives set up that way and am planning on building a bunch of bottoms that are based on 3/4" only. It makes it much easier for me as far as reducing entrances so forth and so on. There is always scraps of 3/4" laying around. Just wondering the pros and cons.
All of mine are 3/4". It lets the mice in more easily, (if you have a bottom entrance, which I don't) but 3/8" won't stop them unless you make some kind of baffle and that works better in a 3/4" opening. The one that is popular around here is a 4" x 14 3/4" (for a ten frame) x 3/8" plywood piece with three 4" long 3/8" thick laths nailed at each end and in the middle. This is slid in the opening to reduce it to 3/8" tall. The mice don't seem to want to crawl the whole 4" at 3/8" tall. My bottom entrances are all closed off completely. Dave Eyre points out that the wax moths seem to sneak in more easily with the 3/4" opening.