Heavy Trucks upped their game and started fitting these as standard to new Western Stars - you may have seen them on some show trucks and on the road.  Complete Chrome ABS Plastic Axle & Nut Cover Kit - 1 Box is all you need for a 6x4.  Add some extra front kits (THUB-FRP33) if you have an 8x4, and some extra rears for your trailers.  These sell out fast!  Great quality, mirror shine, easy to fit, and great price!  The wheel nuts screw in making it harder for people to steal them, and the wheel nuts screw over the hubcap to hold it in place, also securing it from theft, and stopping them falling out on your drive.