This standard specifies the basic requirements for the type, size, technical requirements, signs and packaging of Class A and Class B rectangular spline hobs. The A-class hob specified in this standard is suitable for machining external splines that conform to GB/T 1144-2001, the key width tolerance zone is d10, f9, h10, and the centering diameter has a grinding amount. Class B hobs specified in this standard are suitable for machining external splines that comply with GB/T 1144-2001 and have grinding allowances on the key side and centering diameter. This standard applies to rectangular spline hobs.