PR2 Pro Circuit Air-To-Spring Conversion WP 48 AER hybrid kit. fits Ktm Husqvarna GasGas. includes spring. Kit Description: For riders that prefer a more traditional spring system over air forks, Pro Circuit is now offering a simple spring hybrid conversion cartridge kit that can be easily dropped into your WP AER 48 Air Fork*. The fork cap on this conversion kit comes with an air valve that can be used to add just a touch of air to make the fork a little more progressive through the stroke for the faster, more aggressive riders, or even to compensate for special conditions, such as a mud race. It can also be run at zero pressure for the riders that don't want to mess with adding air in their forks. The kit also offers easy spring preload adjustment without taking the fork all the way apart, letting the fork ride a little higher or lower when needed. This hybrid fork spring system is 100% made in the USA.