They are likely an 8mm and a 14mm.The 1/4chisel is very close to 5/16 and the 1/2 is close to 9/16. That's handy at times. They work well enough that I don't feel bad about spending a fin on them.
The Europeans and others are as bad converting to inch sizes as we are at using metric. Often it is usually the other way around, the 1/4" is really a 6mm and the 1/2" is a 12mm.
jtk