Ok dumb question I know, but are the pulleys measure with a calipers where the belt would meet the surface or are they measured where the belt outside surface becomes flush with the outside diameter guides on either side so that you could measure it across the face of the pulley with a ruler. I have no idea.

 

The outside to outside dimension of the ribs.

 

SOS page has a good image

 

^^^ Typically yes, but you will find inconsistencies with this between the dozen other pulley manufactures out there.

 

cool, thanks