Ball Nut Thread Size

I'm looking to get some ball nuts from MCMaster and it lists a thread
size of 1.173 - 18, the manufacturer lists 1.173 - 18 NS -3A. I
wandered through Machinery 26 and through the KBC tools catalog and
can find things that might work but nothing listed that way.

The gueses I came up with are:

UNEF 1 3/16 18tpi
Metric 30 x 1.5

but it feels very wierd just guessing like this.

Any help?