Stem/Handlebar Dimension?
 

Does anyone know the handlebar diameter (25.4 vs 26.0) of this stem with any certainty?

https://cimg5.ibsrv.net/gimg/bikefor...81c0eb96da.png

-----

would expect 26.0

have not seen any 25.4 from this producer; which certainly does not mean they never made any ;)


-----

The one that I had was 26.0

The aluminum 3Ts I have had, have been 26. The steel ones (Chromix and Chromix Plus) were 25.4. although with steel it doesn't matter so much.

I would bet 26. But the only way to really tell is to have a known and measured 25.4 and a known and measured 26 bar on hand to test.

Looks similar to my ITM listing with its 26.0 clamp.
And I sold a few of these so far. The 3T in gray looks just as nice, IMO.
https://cimg8.ibsrv.net/gimg/bikefor...c8335f2578.jpg
https://cimg9.ibsrv.net/gimg/bikefor...6caa0ab959.jpg

Sorry, i just switched ITM and 3T in my brain. Disregard what I said since it is obviously not directly relevant.

ITM is sometimes marked 25.8, but that is the same as 26.0.

You must be thinking of TTT. ALL of whose pre-31.8mm aftermarket road stems were marked as 25.8mm on their packaging.

ITM, for their part, I believe used primarily 26.0mm sizing. They also produced road stems in 25.4mm, but these were lower-tier products and were primarily (if not entirely) OEM items used on price-point bikes.

Pictured below, this bike's non-original 25.4mm ITM stem features no anodizing, only an as-cast finish that I embellished with a bit of light refinishing.
It has a most-faint ITM logo facing forward that appears to be laser-etched. I sourced it from a swap-meet and it likely came from a lower mid-range Italian road bike.

Modolo similarly produced some 25.4mm Italian-made stems and bars, some (like their "Pilot" bar) were pro quality and just 230 grams.

Edited to say that, at the level of every shop I've worked in, nobody paid any attention as to distinguishing 25.8 from 26.0.
And I can confirm that my caliper has never been able to distinguish between those two sizes when measuring different bars.
It kind of makes sense though that TTT chose their own stated size, simply because they could control the (recommended) use of their own tested-compatible bars and stems by claiming a proprietary size. Not a bad idea in those days, liability- and marketing-wise, when stems too-commonly deformed the bars that they clamped onto, and which could lead to slippage or even failure in the case of lighter heat-treated bars.
Later 31.8mm clamps pretty much solved such reliability issues.

https://cimg1.ibsrv.net/gimg/bikefor...de97ca0665.jpg