road stem or mountain stem
 

Aside from measurements, is there a difference. If the size matches my needs, does it matter if it's road or mountain?

No, it doesn't matter.

However, most road stems now take 26.0mm bars whereas MTB stems use the old 25.4mm (1") standard. 31.8mm (1 1/4", "oversize") bars are becoming more common for both road and MTB and will fit in any stem with 31.8mm handlebar clamp diameter.

Even some stems that have the same dimensions are now marketed as "road" or "mountain". Often, the ones marketed as mountain versions use a beefier construction and so are a bit heavier and stiffer. The differences range from minor to quite dramatic. Using a super feather-weight road stem for some serious MTB'ing might not be a good idea in terms of durability, and using an overly chunky MTB stem on a road bike might make for a harsh ride. However, in between the extremes the differences are often very small.

Thanks, that's what I thought, but needed to know for sure before buying a new one..