CYA or simply CA is cyanoacrylate glue - super glue - crazy glue. It is a bonding agent for balsa airplane construction, but has a multitude of other uses too. I recently had the opportunity to use it to solidify and fill some checks in the grip of a pistol stock I'm making for a buddy. I did the same thing to heal some catastrophic checks in the surface of the back of a 100 pound warbow, turning a piece of kindling into a functional and deadly bow. The super thin glue finds its way to the very bottom of a crack, and when it 'kicks' (sets/cures), completely heals the crack. In soft or end grain wood, after running a screw into the hole, ie: the lower butt plate screw, remove the screw, and squirt some super thin CA into the hole. It will set and harden the end grain of the thread-cut wood, and make it considerably stronger when you return the screw. Make sure the screw hole is completely cured before you return the screw, and apply wax to the screw first, or you will never get the screw out again. Acetone is a solvent for CA.