The Hobie 16 track only fits the H16.
For the rest, the Hobie Wave track is universal. You must add the aluminum section at the top for 17, 18, and 21. That also holds the sail in place much better.
Buy the parts from an authorized dealer. Murrays buys parts from dealers and re-sells.
https://www.hobie.com/dealers/LUFF TRACK 38584000
H18 & 21 MUST ADD 50404101 12" ALUM UPDATES FOR OVER ALL LENGTH (may be hard to find, so another section of plastic track would be required.)
H17 and H17 Sport Mast Requires 50404111 (14.8") update