In multi-pass operation, a round bar of $$10$$ $$mm$$ diameter and $$100$$ $$mm$$ length is reduced in cross-section by drawing it successively through a series of seven dies of decreasing exit diameter. During each of theses drawing operations, the reduction in cross-sectional area is $$35\% $$. The yield strength of the material is $$200$$ $$MPa.$$ Ignore strain hardening.

Neglecting friction and redundant work, the force (in $$kN$$) required for drawing the bar through the first die, is

Observation of a slip gauge on a flatness interferometer produced fringe counts numbering $$10$$ and $$14$$ for two readings. The second reading is taken by rotating the setup by $${180^ \circ }$$ Assume that both faces of the slip gauge are flat and the wavelength of the radiation is $$0.5086$$ $$\mu m.$$ The parallelism error (in $$\mu m.$$) between the two faces of the slip gauge is

To measure the effective diameter of an external metric thread (included angle is $$60$$ degrees) of $$3.5$$ $$mm$$ pitch, a cylindrical standard of $$30.5$$ $$mm$$ diameter and two wires of $$2$$ $$mm$$ diameter each are used. The micrometer reading over the standard and over the wires are $$16.532$$ $$mm$$ and $$15.398$$ $$mm$$ respectively. The effective diameter (in $$mm$$) of the thread is