SUP-1, Understanding Aluminum Extrusion Tolerances (Second Edition, February 1995), explains and illustrates many aspects of the published standard tolerances for aluminum alloy extrusions, such as those contained in Aluminum Standards and Data in both U.S. customary and metric units. Rather than restating the tables, it shows what each tolerance means in practice: how wall thickness, cross-sectional dimensions, straightness, twist, flatness, angularity, corner and fillet radii and surface finish are measured and interpreted, and how the limits relate to the way a profile is designed, die-drawn and handled. The illustrations make the standard easier to apply when checking first articles, settling dimensional questions with customers, and designing profiles that can be produced economically within the permitted variation.