No guarantee that both ends of a wrench will be at the extreme end of spec.
The 1/2" wrench (Canadian Tire Mastercraft) mentioned earlier is good for most 13 mm bolts at the open and the box end, but the 14 mm (german Dowidat) is only good for 9/16" bolts at the box end.
Again, a caliper will...
Bring out your caliper, it will tell you.
15/16" ANSI spec (23.98 mm - 24.21 mm) will almost always fit 24 mm bolt heads.
7/8" > 22 mm so it will on average give you a loose feel.
13/16" is a lot smaller than 21 mm, but if your particular tools are at the upper end of spec (20.78 mm - 20.98 mm)...
1/4" and 6mm (M6) fasteners has 7/16" and 10mm head size.
When those stubborn M2.5 (head size 5mm) bolts just refuse to budge, you bring out the HEYCO 1/2" 5mm socket - and maybe your 24" breaker bar - they are for real :)
Maybe you already have some of these tools in your tool box?
1/2" (12.7mm) tools are between 12.80 - 12.95mm ANSI.
I have found 1/2" sockets and wrenches around 12.94mm and they give you a very tight and snug fit on almost all 13 mm bolts/nuts - the ones < 12.90mm never fit 13mm bolts.
I simply...