Ben Jackson wrote in
:

Ok, this is a stupid question, but are the inside faces of a machinists
square supposed to be square, or only the outside faces? Or, put another
way, are the blade and base faces both parallel?

Both sides are supposed to be square.


I've got the old "never take two clocks to sea" problem -- I've got two
squares and I piggyback them and I can see light between the blades.
So now I don't know which one is off...

There are different grades of squares. Some are within .000080" (eighty
millionths) and some are only .0008" (eight ten thousandths) and there are
others in between. Now if you have two that are of the .0008" variety, it
would be very possible to see light through them even when brand new. IIRC,
they are classified grade 1-4 or something like that. Then there are master
squares. Of course one of them could be bent or worn, as well.

Dan