Thread callout

Question: What is the proper way to callout a thread?

I've seen it two different ways:

1. 1/4"-20 UNC
2. 1/4-20 UNC (the difference being the ")

Which is correct?
Also, is it required to also call out the drill size before the thread callout?

 

Standards vary by company, so it depends on where you work. I've rarely
used the UNC designation anywhere I've worked and the .250-20 thing just
makes my eyes hurt. :O) I've not read the standard, does it really say
that in there?

Anyway, whatever the company wants is what they get, even if it does make my
eyes hurt.

As far a the drill callout goes, when I was going to school they taught us a
good machinist doesn't need the tapdrill size. Out in the real world,
again, it depends on the company. If they want it, I give them what they
want. I kind of agree with the way I learned it in Tool School though.
Back when I worked in the machine shop, they expected me to learn tapdrill
sizes, so I just figure they still do that.

To answer both questions, I guess the "proper" way is whatever way the guys
who's paying you wants it. :O)

Have fun,
Dave

callout?