[Mr V]

10-24, 10-24 and 10-24. For lengths 1/2" to 1 1/2 or 2" is a good range. Make sure the nuts are nylocks.

10-24 is plenty strong enough and having 1 size means it is less likely that someone who doesn't know a lot about using fasteners will put a #10 nut on a #8 bolt. I recommend the coarse thread (-24) since they are harder to cross thread than fine thread (-32).

Note many of the COTS items do use 10-32 and 8-32 so a few of those in shorter lengths are not bad to have on hand, just store them separately and have them specifically labeled as to their uses.

#10 is nice in that you can use the same hole size for those and 3/16" rivets. So you can bolt things together until you are finalized and then switch to rivets when you know that you are using that configuration or it isn't likely that you will need to remove that item for service.

So ask for some high strength 3/16" rivets too.

1/4" is overkill for most applications and #8 are strong enough for many applications but having one size fits all makes for less items to stock and less confusion.