The set has two protectors for the rear hub (bigger ones) and two for the front hub (smaller ones) plus adaptor rings if required.
It is also possible to install this protector on earlier ktm models from (2003-2006) but you need to update your wheel spacers with the newer design also available from 4mxracing.net part number: front 4mx-wso1, rear crt-074mx
The instalallation is very simple, you just need to remove your wheels, and even with the spacers on you need to squeeze the protector in to the grooves on the wheel spacers.
Make sure you have the hubs and spacer cleaned before you install the protectors.
If you have one of the later ktm, husqvarna or beta models, you need to use the supplied spacers.
Please notice that if the bike has a front disc protector you shouls not install the protector on the disco side.