Got a year and application?  For the cars, the belts were ½” wide thru 1956 and went to 3/8” wide starting in 1957.  Trucks and pickups are specific to year and accessories.  With the original application in hand, your local parts store should be able to provide the factory  recommended belts assuming the pulleys are stock.

Lorena, Texas (South of Waco)

could  someone please give me a number for the  gen\water\crank pulley Belt..

    Looks like the distributor is original  a  cot    12127     with  00 below...
I don't know if the cot means anything or the 00