Like DB said not only are they no problem but really are preferable. Particularly when you start using a starter if not already, the spinner nut provides for a much better starter to spinner interface and are safer than using a starter on a propeller and washer/nut combination.

Great Planes and Dubro sell cone shaped ones in both brass and aluminum. These fit most starters better than the ones made to look like a Hamilton Standard propellor hub. Also they are far better than plastic spinners that can have safety issues and always develop that ugly black ring from the starter. To my way of thinking they are far more attractive with a functional machined look on any airplane that is not exact scale.

For what its worth the threads on your crankshaft are 1/4 28's

John