Dụng Cụ Đo Hành Trình Phuộc Coil MTB

The parts are printed flat side down. PETG preferred. Most likely works on PLA as well.
It's made so that it's super easy to print.

There is a hole on the end of the rod. I used a normal computer HDD screw there to keep it in place.

A suitable size o-ring is needed as well.

I could only test this with a Rock Shox Super Deluxe Coil Ultimate shock with Nukeproof spring.
If it doesn't fit your coil, try enlarging it it the slicer a bit. I would recommend printing only one of the end caps first andthen test if it fits.
When mounting, make sure the rod won't hit the frame or any part of the shock.
 

After a ride, you can measure the distance of used travel from the rod. For example, I measured 53mm on my first test ride while the full travel of the shock is 60mm.