ISO 521:2011 specifies the dimensions of machine chucking reamers with cylindrical shanks and Morse taper shanks.

It deals with the following types of reamer:

• machine chucking reamers with cylindrical shanks in the range from 1,32 mm to 20 mm diameter;
• machine chucking reamers with Morse taper shanks in the range from 5,30 mm to 50 mm diameter.

For each type of reamer, ISO 521:2011 gives two tables, one showing preferred sizes with corresponding dimensions, and the other being a general table set out as functions of diameter steps. Provision is also made for tolerances on lengths, cutting diameters and the diameters of cylindrical shanks.