The length of profile, selected for the purpose of making an individual measurement of surface texture is known as

38) You have been given an aluminium block in which hole is to be drilled. From the tool manufacturer's cutting speed chart, 77 m/min speed to be used for aluminium. The r.p.m to be used for 10 mm drill bit is

39) The approximate depth of thread for M8 x 1 is

40) General formula for the length of the snap-head rivet is (t - thickness of the joint to be riveted and d - diameter of the rivet)

41) Derivative of -sinx with respect to x is