Figure 12. Chart showing the relations among phi sizes, millimeter diameters, size classifications (Wentworth, 1922), and American Society for Testing and Materials and Tyler sieve sizes. Chart also shows the corresponding intermediate diameters, grains per milligram, settling velocities, and threshold velocities for traction. cm/sec, centimeter per second; m, meter; mm millimeter; µm, micrometer; ", inch.