Understanding the Spec and Getting It Right
I keep running into people who order Ar 600 8 19 without really reading what the spec covers first, and then they wonder why their application doesn't hold up under stress. It's a straightforward tolerance standard for aluminum extrusions in the 6xxx series, but the details matter more than most people give them credit for. The "600" refers to the aluminum alloy series — 6061 and 6063 are the most common grades you'll see here, both heat-treatable with magnesium and silicon as the primary alloying elements. The "8 19" portion describes the dimensional tolerances: a nominal tolerance band of 8 thousandths of an inch on general dimensions and 19 thousandths on specific critical features, depending on the cross-section size and whether you're measuring width, thickness, or straightness. This is an industry-standard tolerance class, not a military or aerospace-specific one, which is why you'll find it referenced in architectural and general fabrication catalogs more than in high-stress structural work. I worked on a project last year where we were machining brackets for a custom fixture, and I specified Ar 600 8 19 thinking it would give us enough precision. The supplier delivered material within spec on paper, but when we went to assemble, three out of twelve brackets didn't stack properly. The issue wasn't the material itself — it was that the tolerance class allows for angularity deviations that only show up when multiple pieces are mated together. We ended up trimming each bracket by hand with a file and a square, which added about 45 minutes of labor per unit. After that, we switched to specifying a tighter tolerance class for mating surfaces and only used Ar 600 8 19 for non-critical dimensions.
How to Source It Without Losing Your Mind
The actual download or specification sheet for Ar 600 8 19 isn't something you typically find as a standalone file you can just grab off a website. It's embedded within larger standard documents — mostly AWS and ASTM references — and the most reliable place to pull it from is the Aluminum Association's online database or through your material supplier's technical library. If you search for "ASTM B221 Ar 600 8 19 tolerance," you'll land on pages that summarize the key numbers, but the full table with all the cross-sectional size breakpoints is usually behind a paywall or requires a free registration with the organization. Most extruders and distributors like Metal Supermarkets, Omya, or local aluminum service centers will send you the relevant spec sheet on request. It takes them about a day to pull it together, and they'll usually email it directly. That's faster than fighting through any of the free online repositories, most of which have outdated or incomplete tables.
Pitfalls That Nobody Talks About
One thing that catches people off guard is the difference between the nominal tolerance and the actual tolerance at different cross-section sizes. The 8 and 19 values aren't flat across the board — they scale with the dimension you're measuring. A 2-inch wide extrusion and a 6-inch wide extrusion both fall under Ar 600 8 19, but the actual allowable deviation is noticeably wider on the larger piece. If you're designing for tight assemblies, you need to check the specific tolerance for your exact dimension, not just assume the "8" and "19" apply uniformly. Another gotcha is the temper designation. Ar 600 8 19 talks about dimensional tolerance only. It doesn't specify the temper — T6, T5, T4 — and that changes everything about the material's strength and machinability. I once received 6063-T4 when I needed T6 because the order didn't specify temper explicitly. The parts machined fine, but they couldn't handle the load requirement, and we had to scrap about $800 worth of material. Always include the temper in your purchase order, even if your supplier thinks they "know what you mean." If you need something tighter than Ar 600 8 19 can offer, especially for precision mechanical assemblies, you're better off looking at CNC-milled aluminum from bar stock or going to a tighter extrusion tolerance class like MIL-S-600 or the equivalent ISO 1127 tolerances. They cost more and lead times run longer, but you won't be filing brackets at 11 PM trying to make them fit.
