A little history from the wiki:
History- The Perfect 360 started out as an aftermarket add-on kit for Wico leafswitch joysticks. Models were later added to the product line to convert Happ Super, Competition, and Ultimate sticks, and possibly others as well. Happ eventually bought the rights to the P360 technology, and discontinued the kits. Happ began producing a complete stick instead, with the top half of a Wico joystick base (no longer sold by Wico by then) mated to a P360 bottom half.
Interchangability- P360 handles and Wico handles have been found to be interchangable. There are also replacement handles available from SlikStik. Wico Pear-top sticks used the same pivot cones and spacer sleeves.