AA claims those "Nut Master" wrenches from New Britain[/URL] were actually simply intended as an improved open-end design and patented in 1954. An early version of a flank-drive tool...
Here's a picture of mine and a regular NB flare nut wrench of the same size.
I only used mine on flare nuts and tubing nuts. It works great for that. I break them loose with a regular flare nut wrench and then use the New Britain one. I never used it for initial breaking or tightening because it's not as thick as the regular flare nut wrenches and it only grabs on four sides.
It's a lot easier to be careful with tubing initially than it is to fix it when you mess it up.
It has a ratcheting like action and is a lot faster than an open end flare nut wrench. You only have to tilt the wrench backwards about 1/3rd of the way off of the nut and then you can rehook it. I always assumed that it was designed for that purpose. You can eat an open end wrenches lunch with it for speed.
Now, I can see where Snap-on got the flank drive idea from. For an open end wrench, it contacts four sides and well back from the edges.
Thanks for the info on this. I'd almost swear that NAPA was originally selling these as tubing wrenches though. Maybe I'm wrong about that though, it's been a long time.
Maybe someone has a New Britain catalog that has these in it.
WoD