I've got a Leigh D4, the thinnest pins you can do, measured at the widest point is 1/4" but only in material upto 1/4". If you go upto 5/16" pins then you can use 3/8" stock or 3/8" pins will work on stock from 1/4" to 1/2" thick. There are several larger sizes as well, this is for through dovetails.
All the half blind dovetails are 1/2" withe the angle changing as they get longer for thisker work.
Do you mean thickness of wood stock used or bit size?? I know you can go down as low as 3/16" for timber thickness with the through dovetails.You can cut 1/4" wide dovetails using the 50-8 bit.