Stem diameter question Changing to an adjustable Ritchey stem on my Trek 7.3. My bars are 25.4 and the stem I'm looking at is stated to be for 25.8-26. With this being half a millimetre bigger, will it still fit ok?

Many thanks!
No, it doesn't seem like much, but that stem won't fit your bars without a shim. Very wise of you to ask. Nitto (and probably others) make shims for just this situation. They cost about $10 US. The old standard for road bikes was 25.4 mm (for the most part), but there seems to be a move towards 26.0 mm.