Cup and Cone Bottom Bracket Question
 

I know pretty much nothing about vintage bottom brackets. Here are a couple pics of the existing bottom bracket from a bike I recently picked up. Is this definitely an English threaded bottom bracket? There is an "F" stamped on the bottom bracket shell, which I took to mean "French".

https://cimg0.ibsrv.net/gimg/bikefor...735afdbd4c.jpg
https://cimg4.ibsrv.net/gimg/bikefor...9f34eaa31f.jpg

Not French
https://www.sheldonbrown.com/gloss_bo-z.html#bottom

The bike is the unknown Austro Daimler. Mine had a very normal 68mm English bottom bracket. That one is English too.

Yep. It's the mystery AD. And thank you everybody. It's a relief that I don't have to deal with a French thread on this frame. The current bottom bracket is in fine condition, but I was going to search out a backup if it turned out to be French.

Now I wonder what the "F" on the frame stands for........

The F on the frame is confuzzling me a bit. According to this: My Austro-Daimler "Vent Noir II" Bicycle And Brief History of Steyr Daimler Puch, the F SHOULD indicate that the BB is french threaded, but the Shimano that's currently in there says otherwise. The F should also be on the underside of the lug. The way I knew mine was English was by the knurling on the Nervar lockring, but that doesn't apply here. I would pull the fixed cup to be sure. I would bet on it being English, but Velo Orange sells french threaded bottom brackets.

It wouldn't be the first time something marked one way was built another way. I could see something forcing a BSA bb into a Swiss shell, but French is right threaded on the DS.

Easy enough to take out the NDS cup and look, though.

Yeah. If I can find the appropriate tools in my box, maybe I'll remove the lockring while the bike is still fully disassembled, just to be sure.

Is it okay to remove just the fixed cup to check, or do I need to start on the opposite side?

Start on whichever side you want, the bike shouldn't care.

Cool. Thanks.

"1.37 x 24" is English thread. The "F" on the shell may indicate who brazed the frame. At least that's how we did it at Trek.

Regardless of the 'F', it's definitely not a French-threaded (or even a Swiss-threaded) bottom bracket: those have 35mm x 1 threading, and are usually marked as such. Yours being marked with the English threading information (1.37 x 24) absolutely identifies it as having English threading.