quill stem sizes

[wheeliebin]

I need to replace the quill stem on an old Trek 800 MTB, but I'm a bit confused by the dimensions of stuff advertised e.g. 22.1mm, 25.4mm, 1", 1 1/8". Adverts don't always make it clear what the measurement applies to, and also sometimes confuse it with the handlebar clamp size.

The existing stem measures exactly 25.4mm/ 1" dia, am I right in thinking this is for a 1 1/8" steerer tube?

Thanks

 

[iluvmybike]

No - its a 1" steerer surely

 

[wheeliebin]

I think I may have answered my own question here, don't know why I didn't find this before. From Wikipedia (citing Sheldon Brown):
On the other hand, a quill stem must be sized to match the inner diameter of the steer tube. Thus a quill stem made to fit a 11⁄8" steer tube has an outer diameter of 1". For 1" steer tubes the quill diameter is most often 7⁄8" (22.2 mm) but some older American bicycles used 21.15 mm. Some older French bicycles used 25 mm steer tubes with 22 mm diameter quill stems.[6]