Square threads are usually found on spindles of bench vices

A basic shaft is one whose Upper deviation is zero
Upper Deviation: It is the algebraic difference between the maximum size and the basic size. The upper deviation of a hole is represented by a symbol ES and of a shaft, it is represented by es.
Lower Deviation: It is the algebraic difference between the minimum size and the basic size.

Lapping is a machining process in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine. Lapping process gives best surface finish.

Area of a triangle having side 6cm, 8cm and 10 cm is 24 square centimeter