6) What is the purpose of vertical rib with round shape on its top in bottom frame of window?

7) Which screw thread of 55 Degree included angle and depth of thread is 0.6403 p is used in general engineering fasteners?

8) Which screw thread of 47? Degree included angle is used in electrical and instrument screws?

9) Which is the material used in construction of navy boats?

10) What is the purpose of glass lining of valves, pipes and pumps?