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?

11) Which type of packing is used for side rolling and folding hatch covers?

12) Which type of glass is used in manufacture of artificial gems, electric bulbs, lens and prism?