I picked up a tap wrench at a estate sale today. It looks like a GREENFIELD. It is marked,

OK.

MADE IN USA.

NO. 15

012

It was painted red at one time, with very little paint left. It opens up to 5/16. All steel with knurled handles. 11 inches OAL with the jaws closed. Seems well made with close fitting parts. I have never heard of a tool brand called OK. Any info would be helpful. Thanks,
EvilDr235

Neither have I, but it clearly had at least a little more marketing success, based on your example there, than its competitor, "NOT OK."

OK was a Greenfield (GTD) brand.

Greenfield, yea. I seen a slight mention somewhere else that it might be related to Greenfield. Must have been a economy line for them.  They seem to be well made, but no color case hardening. It has some minor surface rust that some steel wool and some oil will fix. I will add it to the hoard and use it. Thank you all for your time and effort.
EvilDr235

After looking thru other tap and die tools I have, I discovered I also have two OK. die handles.  I also found CARD and a BAY STATE brand die handles.

EvilDr235

Greenfield Tap & Die (GTD) of Greenfield, Mass, made tap/die products under several brand names, including OK and Little Giant.  I don't know that OK was the economy line; if it was, it was certainly better than most readily available taps and dies today.

GTD is still alive as part of the Widia group, a subsidiary of Kennametal:

like I stated above, I believe the OK brand is well made, but with a lessor finish on them. I have seen lots of sets of Little Giant brand taps and dies. I buy them once and awhile as single pieces. Little Giant seems to be very popular and most of time very costly. Also most little Giant sets I see are for tapping and threading larger things that I don't work on that often. Most tapping and threading I do is 1/2 inch and smaller. I will buy any size if the price is right. Also I try to avoid most Asian imported tools. I do like German, Swiss and English made tools.

EvilDr235