The devices which are used to prevent the escape of foul gases inside or outside the house are called

27) Among the tools listed below, the ideal tool to tighten an HSH screw is

28) An M12 bolt has

29) For an M12 x 1.75 bolt with single start thread, how many threads will be engaged if the bolt is inserted through a length of 35 mm?

30) For a double-start thread