Bryan and Allan,
If the spinner is for a 3-blade prop, and/or has a front center bolt attachment instead of Goldberg-type snap-on or various other-brand 2 screws into a backplate as mounting, an adaptor nut is needed.
As Bryan suggests, such nut is tapped for the engine shaft at one end, and for the spinner mounting screw at the other - front - end. Spinners do look "cleaner" without the two screw access eyebrows we're so used to. Tru-Turn spinners are not cheap, but there may be a suitable adaptor available from them. Some of the older spinner mfrs may still offer nut and bolt parts for theirs.
Luck, Bryan!