And {HEAD ~ a rotary drive torque} of {TAIL ~ a level} less than said maximum engagement torque but greater than the reduced engagement torque is operative to impart an incremental thread advancing rotary drive, during such intervals as the engagement torque is thus reduced 
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And { HEAD ~ a rotary drive torque } of { TAIL ~ a level } less than said maximum engagement torque but greater than the reduced engagement torque is operative to impart an incremental thread advancing rotary drive , during such intervals as the engagement torque is thus reduced
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH