138) To enable a nut to fit properly on a bolt of square threads, the width of the internal square threading tool should be

139) For cutting acme threads, the threading tool should be ground to an included angle of

140) The tip of a cemented carbide tool is joined on the shank by

141) To cut 20 mm internal square thread with a pitch of 2.5 mm, the core diameter should be

142) Which one of the following materials for lathe cutting tools can be forged to any desired shape ?