I use wheel lock collars. They are sold by Du-Bro. http://dubro.com/hobby/

Specifically, this part, 12 to a bag, http://www.shopatron.com/search/101....&a=8439&qt=all
That should get you to the part or at least a description of the part. They are sold by all hobby shops that service aircraft hobbies, so your favorite on-line supplier will have them. The shipping charge from Du-Bro is $7 so the little collars get sort of expensive if that's all you order. Maybe using the description and Du-Bro part number, you can combine this order with something else from your on-line shop and get the cost down.

Does that help?

Soloboss