Genuine Sanitaire also made to fit many Eureka Models 
You can distinguish Genuine Belts by the markings on the belt. Genuine Belts have the part number 30563B and the description EU STYLE RD imbedded in the rubber. If the belts you receive do not have these markings they are not genuine. 
Manufactured by Sanitaire and Designed to fit all Sanitaire Uprights where the belt rides in the center of the brushroll 
This Genuine Belt has also described as part number 30563A, 30563B, Style Type RD, 52100, 52100B, 52100C, 52100D, These genuine rubber belts fit all Eureka and Sanitaire upright vacuums with the round tube type belt.