One of the precision instruments used to check the dimensional accuracy of an external 'V' thread, is a screw thread micrometer. Which one of the following elements of a screw thread is checked with screw thread micrometer ?

Grade 00

Slip gauges are graded according to their accuracy as Grade 0, Grade I and Grade II.
Grade 0 is used in laboratories and standard room which serves as standard for periodically checking the accuracy of Grade I and Grade II gauges.
Grade I is of higher accuracy and used in inspection departments.
Grade II is intended for use in workshops during the actual production of components, tools and gauges.