Missouri trapping regulations might tell u all you need to know.

SNARES-

Snares must comply with the following:
-Be set underwater
-Have a loop 15 inches or less in diameter when set
-Have a stop device that prevents the snare from closing to less than 2 1/2 inches in diameter
-Be made with cable that is between 5/64 inch and 1/8 inch in diameter
-Have a mechanical lock and anchor swivel.

CABLE RESTRAINTS-

When used correctly, cable restraint devices hold animals alive and allow trappers to release non-target animals unharmed. The devices can be used to take furbearers from November 15 through January 31.

Cable restraint devices MUST:
-Be made of stranded steel cable, not greater than 5 feet long (not including extension, with a diameter of not less than 5/64 inch and equipped with a commercially manufactured breakaway rated at 350 pounds or less, a relaxing-type lock, a stop device that prevents it from closing to less than 2 1/2 inches in diameter, and an anchor swivel.
Note: Compression-type chokes and other mechanically powered springs are prohibited.
-Have a loop size of 12 inches diameter or smaller when set
-Have the bottom of the cable loop set at least 6 inches or greater above the ground
-Be anchored solidly or staked in a location not allowing entanglement
-Be checked daily.
Cable restraint devices must NOT be:
-Capable of extending to within 12 inches of a fence
-Set using a drag
-Set with a kill-pole
-Used within 150 feet of any dwelling or driveway leading to a dwelling.

It says I need a stop to keep it from closing less than 2 1/2 inches. Would a regular nut work for that? And what kind of "mechanical lock" do I need to get?

Something like these are what you need, if you're not using them under water.... https://schmittent.com/product/mo-pa-wi-cable-restraint/

If I'm not mistaken you have to take a Cable Restraint class in Mo. before you can use them as well.