Jupiter French Horn repair parts.  Many older versions of the stop arm screws use a smaller diameter screw.  Good news is we stock both.  The newer version has a larger diameter and course threads.  The older screw is smaller diameter and has fine threads.  The older version is also a current "rotor lever saddle screw" used on the CH-800 and JHR-852 horns.  Contact us if you wish to verify your models' fit.