The fractional T-slot family uses an inch measurement system (imperial). 80/20 currently offers 57 profiles in fractional units with two standard series: the 10 series and the 15 series.
10 series profiles are based on a 1 inch standard while 15 series profiles are based on a 1.5 inch standard.
The metric T-slot family is measured in meters or millimeters (mm). 80/20 currently offers 51 profiles in metric units with five series; 20, 25, 30, 40 and 45. The dimensions of the metric profiles each coincide with the series: 20 series profiles are based on a 20mm standard, 25 series profiles are based on a 25mm standard, and so on.