> 25 thousandths would be sloppy, a nominal clearance hole for a 1/4x20 bolt is about that much.

Isn't that 0.250 which would be 250 thousandths?

No, they're talking about the clearance, which is the difference between the diameter of the bolt itself (1/4") and the diameter of a hole in which the bolt loosely fits (a couple hundredths of an inch bigger than that).