48 attached to the lower block of the compound tool rest 20 the length of the moment arm bc is calculated to provide a linear movement in the direction indicated by arrow 50 equal to the amount of lead being added to or subtracted from the standard thread setting thus for the exampe of 39 threads per inch given above the moment arm bc would be adjusted to provide 0 00064 inch addition to the lead for 40 threads per inch in order to quickly set the amount of lead into the tool adapter a calibrated scale 52 is mounted on the lever arm 40 having a center o position a pointer 54 indicates the relative position of the regulator block 38 and hence the pivot pin 36 for adding or subtracting a predetermined amount of lead the scale 52 may be calibrated to provide up to a 10 or more addition or subtraction in increments as small as one one hundredths of one percent thus for a setting of say plus 1 01 on the calibration scale there would be a 1 01 addition to the standard lead set into the lathe the arrangement of scale 52 and pointer 54 is preferred but could be reversed and of.