This Poppet Valve will only fit Ball Lock Firestone Challenger V & VI, Super Challenger.
This is a brand new poppet. Keep in mind that many kegs have had posts switched by soda distributors and other owners over the years. Look at your poppet valve and see if it matches before ordering.
If your poppet does not match this could mean two things; Either post has been switched and you need a different poppet valve or the post is correct and someone put the wrong poppet valve in your post.