21) Which type of thread is used in screw jack spindle?

22) A thread is represented as M12 x 1.5. What does represent the letter 12?

23) Which method of holding is used for lengthy work to avoid over hanging?

24) Calculate the change gear required to cut 4mm pitch thread in a lathe having lead screw of 4mm (lathe stud gear (driver has 50 teeth)

25) Calculate the change gear (driver gear) if driven gear has 120 teeth to cut 3mm pitch on a job using lathe having 6 mm pitch lead screw?