Which one of the following instruments is widely used to check and calibrate geometric features of machine tools during their assembly?

The flatness of a machine bed can be measured using

A metric thread of pitch $$2$$ $$mm$$ and thread angle 60° is inspected for its pitch diameter using 3-wire method. The diameter of the best size wire in mm is $${60^ \circ }$$ is inspected for its pitch diameter using $$3$$- wire method. The diameter of the best size wire in $$mm$$ is

In an interchangeable assembly, shafts of size $${25.000^{\matrix{ { + 0.040} \cr { - 0.010} \cr } }}\,\,mm$$ mate with holes of size $${25.000^{\matrix{ { + 0.030} \cr { + 0.020} \cr } }}\,\,mm.$$

The maximum interference (in microns) in the assembly is