Which one of the following thread forms on bolts and nuts is meant for general fastening purposes ?

21) Which one of the following screw thread elements is not checked with thread ring gauge ?

22) Which one of the following elements of an external screw thread cannot be measured directly with precision instruments ?

23) Which one of the following statements is correct with respect to the spiral fluted taps ?

24) The shape of the frame of thread snap gauge is in the form of :