Outer diameter micrometer the external dimensions measuring instruments, measure the distance between the two sides of the square fe by use of helix principle. Outer diameter micrometer is mainly used for measuring a variety of external dimensions. Diameter micrometer dividing value is0.01mm, the upper limit of measurement range is not more than 300mm, divided into a 25mm per specification. Such as 0-25mm, 25-50mm ...... and so on.