Lug Nut (Wheel) Lock Size

I'm shopping for lug nut locks for my 550, similar to these. For those who have them, what size thread should I be looking for? Does anyone have a recommendation for a specific lock?

Thanks

 

Order these from Amazon 24194 Chrome Cone Seat Wheel Locks (1/2" - 20 Thread Size) - Set of 4

http://www.amazon.com/gp/product/B000COS074/ref=oh_details_o00_s00_i00

 

Gary,

Awesome, thanks a bunch!

 

Oh Krap... I ordered some without checking to see if they'll fit.. coming as a Christmas pres to myself... didn't realize one needs to check the fitting/sizing... Gawd, hope I get lucky.. heh, ouch..

Whew, got them...
McGard 74042 Chrome Cone Seat Trailer Wheel Locks (1/2"- 20 Thread Size) - Set of 2
done...