I recently purchased a new PS pump belt, size 10x1075 and it's almost 11mm
wide. Check out the photo below comparing two belts, both ContiTech, both
the same part number but the new one on the bottom is almost 1mm wider than
the older one (measured with a micrometer). If you look closely by my thumb
you can see where the edge is starting to fray due to the incorrect fit.

http://i.imgur.com/utXtKpK.jpg

-Mark
87 Syncro Westy