½" x 3¾"
Steve, does it have to be that long? The metal stems that come in the tubes from the vendors are 1/2 inch, but are about an inch shorter than the one you show.
Maybe somebody can cut the stem out of an old reproduction metal stemmed tube that is too far gone to patch and send it to you. I used to have a couple of the repro stems, but I can't find them, I must have sold them or given them away already.
Unfortunately, the currently available bridge washers are flat, no raised surface like the one you show. I suppose with a press and some tooling, you could press a circular dimple into a current flat washer.
I've got a bag full of 777's or 725's -can't remember which! I'll look when I get home tonight.
If I have 725's I can bring them Saturday if you're going to the winter clinic in Hutchinson.
777's are what Ts came with originally, so if you bring them, they'll get lots of interest.
Actually, this stem from a modern tube is an exact size match for the 725. This is where I got the ½" x 3¾" measurement. The only original I had is now in a tire, and I could use at least three more. I can use the 777's for my nickel era car, but the brass nuts and covers I have for the 1915 don't fit them.
Brian, yes, I aim to be there.
I stand corrected, must be the closeup photo, for some reason the stem you showed looked longer than I remember.
Anyway, hopefully I'm not the only person that saved the metal stems out of modern tubes when they have a blowout or cut and somebody will be able to hook you up with a few.
I sent you a pm on what I've been able to find so far..
If you want a 725 buy it! It is not correct for a Model T.