i had a 34q/r bought a new half nut to stop it jumping direct from record in the early 90's,they told me it was guaranteed unbreakable & from my description dated it pre late 50's after few years started jumping again,tried to give it more tension by winding the serrated nut,assumed the lead screw was worn so thinking it would cost too much i welded the nut to the screw-still gripping after 21 years.