i cant really tell the exact situation from that picture.... is it an actual track hub? or just an old 5speed hub that had a cog threaded on? are the threads at all damaged now? If it is a track hub youll use a track lock ring.. remember its reverse threaded. If it is a 5speed hub, you can get away with using a bottom bracket lock ring if you cog is large enough that the chain doesnt hit the lock ring. But yea, give us a little more info and well help out more...