I am designing a drive screw and nut for a new tool. I am familiar with standard acme threads, but after researching lead screws, they use a class C or centralizing acme. From reading the handbook, it seems that the major dia's are different than the class G acme. I cant find inserts for a class C in the few places I have searched. Has anyone machined or specified class C acme screws and nuts? If so, are there inserts or do you end up having to tweak the class G? I found the formulas where I can calculate the thread dims but I am more concerned about making it as simple as possible for my machinist which has never machined a class C. thanks for feedback