Master cylinder tapped hole for brake line fitting

[slk25]

Hey Guys,
Newbie here.
I am changing out a single bowl master cylinder on a 66 hardtop with drum brakes. The replacements I have tried from O'reilly's and Summit seem to have a different thread for the fitting than the unit I pulled off the car.
Are new parts tapped metric or what?
I had a similar problem with a wheel cylinder that required a 10mm wrench to open the bleeder versus the 7/16" wrench used on the other bleeder screws.
Any body know of a tap dimension change or some place to get a gauge to check the size of these out?

 

[Grabber70Mach]

This might help:

http://www.ultrastang.com/products5.php

Also Welcome aboard

 

[slk25]

thanks allot.
Turns out the Summit Racing master cylinder is also 7/16-20 thread like the old one.
The O'reilly unit was not that big in diameter, possibly 10mm instead.