13) Which machine is used to cut helical groove on a workpiece?

14) Which gear is classified according to the tooth surface and use

15) Which type of bevel gear is used to connect shafts that are at an angle but not intersecting?

16) What is the machine element with a surface or groove formed to produce a motion to another part follower?

17) Which element having a projecting part of the cam imparts a reciprocating motion to the follower?