Some bridges are drilled inside and out, so be sure your bridge has metal at the bottom to stop the spring from falling out. Some of my guitars will need a screw at the bottom of the hole but that's not a big issue, zinc is a soft metal, it's easy to make a thread for a screw.
The spring does keep the trem bar in place, but it made a little scratchy noise so it needed a bit of sanding on each tip, and a drop of oil. The "spring" compresses and does not expand back into its original shape but that doesn't matter, it does its job.