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Modifying a cross slide nut for taper turning


I bought a Boxford model C cross slide lead screw at auction , and checking if it would fit my South Bend model A , noticed that the nut for taper tuning was in two parts , after measuring the height made a spacer and chopped off the top of the nut drilled and taped it , then turned a bolt to fit when I make my taper turning attachment remove the bolt and use the compound to feed in . 

Trimmed the spacer this morning and fitted the nut to the cross slide , in the most worn part of the leadscrew I had 12 thou backlash , compared to over 50 thou previously but hears the thing the old nut is tight on the Boxford leadscrew , I have cut a thread to fit the Boxford nut from silver steel but the South Bend nut doesn't fit , is there a difference in the specification for acme thread in Brittan and America ?

There is a differnece in flank angle. Metric trapezoidal thread has 30 degrees and acme is 29 degrees. However, I have seen on lathe dial screws odd combinations on lead, diameter and included angle. Sometimes the metric and imperial machine has basically same diameter leadscrew, but lead is different and ofcourse dial grating.

They are both imperial 10 tpi and 7/16" diameter , the Boxford was converted to metric hence  the spare leadscrew , the tool I cut the tread with fits both threads but not enough to judge accurately , but I am pleased with 10 tou backlash and a spare .   


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