Some combination locks suggest not setting the last number to anything too close to zero but the specifics depend on how the lock is built. It’s hard to explain why, but if the last wheel starts to line up around the same time the fence wants to drop in, the mechanism can get “confused.” I’ve always had trouble visualizing this and I really ought to try setting one up with a forbidden number just to see what might happen.
Anyway, just to be safe, I might suggest avoiding anything between 80 and 20 unless somebody else has a better guideline for this particular style of lock.
Other common suggestions (if you’re after actual security rather than having a neat display piece) include avoiding numbers that end in zero, rising/falling combinations, and using birthdays etcetera.
