Stub shaft adapters are available to fit FSO and HPI clutches from size 400 through 1027. The stub shaft adapters may be used to mount gears, pulleys, or similar attachments when the item to be mounted is too small to mount on the O.D. of the clutch, and to mount couplings when the customer desires to use a coupling other than the Formsprag-Formflex clutch coupling assembly.