> it seems there is at least three, not counting drone foundation.
Go to my site, www.bushfarms.com
and you'll see quite a few pictures of foundation with a tape on them to measure them.
> There is the 4.9 mm, and a size which Kelly currently sells aparrently as "standard" which seems to measure 5 cells per inch horizontally.
I'm not aware that Kelly has 4.9mm although I see they are selling a mill that is 4.9mm. As far as I know only Dadant makes 4.9mm wax and and Dadant and Brushy Mt. sell it. But then I haven't bought Kellys medium brood for a while and haven't measured any. I only have Kelly's 7/11 wich is 5.7mm.
> Is there a larger size supplied by some of the other suppliers?
Almost all medium brood wax foundation is 5.4mm unless otherwise billed and only Dadant and Brushy Mt are selling 4.9mm wax.
Pierco varies in size depending on if it's deep or medium and if it's frames or sheets. I have several of these measurments on my web site.
> I seem to have seen the "5 per inch" referred to as an "old" size.
That was the standard at the turn of the century. Which would be 5.08mm.
Any fully drawn plastic has the cell wall there so you have to allow for that. Since a standard "bee drawn" wall is .1mm you have to factor that in.
PermaComb, is the equvilant of 5.1mm when you take the cell wall thickness into account.
I use a lot of natural comb (foundationless frames and top bars) I see natural sized worker cells down to 4.4mm and not much that is over 5.1mm.