Billet Aluminum Parts

What “billet” actually means

Billet just means the part starts as a solid piece of aluminum, a block, plate or length of bar, and the shape is cut away from it. In the trade the word is used loosely for bar stock and plate, which are rolled or extruded to size before anything is cut (source 1). The part itself is not poured into a mold.

That starting point is the difference from a casting. Cast aluminum alloys generally have lower tensile strengths than wrought alloys (source 2), and the pores that form as a casting solidifies can reduce strength and fatigue performance (source 3). Strength also depends on the alloy and its temper, so a billet part is only as strong as the grade it is cut from.

For the aftermarket, “billet” has become shorthand for a part cut from solid. It is the performance corner of CNC machined aluminum parts more broadly. Send a model or a custom billet design and the team will quote it from the solid.

The billet aluminum parts we quote

Common requests run across the performance and motorsport world: valve covers and coil covers, billet wheel spacers and adapters, shifter knobs and shift plates, fuel and gas caps, catch cans, pulleys, brackets and mounts, caps and fittings, and weld-in bungs that thread or weld into a tube or tank. One-off show pieces and small batches for a product line are both normal orders here.

Round parts like spacers, caps, knobs, and bungs suit CNC turning; covers, plates, and brackets suit milling; many parts need both. You send one model and get one quote that covers every operation the part needs.

6061 vs 7075 for billet parts

6061 is one of the most commonly used general-purpose aluminum alloys (source 2). The 6000 series is described as easy to machine and weldable (source 2), and 6061 stays corrosion resistant even where the surface is abraded (source 4). Start there for covers, spacers, and trim unless the load calls for more.

Reach for 7075 when the part carries real load. The 7000 series can be hardened to the highest strengths of any aluminum alloy (source 2), and 7075 is one of the most commonly used alloys for highly stressed structural applications (source 5). It is also described as vulnerable to stress corrosion cracking, and the T7 (T73) temper reduces that susceptibility (source 5), so name the temper on the print.

If you’re not sure which grade a part needs, say what it does and the quote comes back with a recommendation rather than a guess. See the 6061 vs 7075 comparison for the full breakdown.

Finishes and getting a quote

Anodizing, clear or color, gives a decorative, corrosion-resistant oxide finish (source 6); powder coating is quoted too. A finish called out on the print is quoted with the part, so name it when you send the files. Then send a STEP model and a drawing through the quote form with material, quantity, and finish, and a real person prices it in 24-48 hours, free design review included.

Sources

All accessed 4 October 2026. Where a figure here differs from your print, the print governs.

1. Wikipedia, “Bar stock”: en.wikipedia.org/wiki/Bar_stock (bar stock, colloquially billet, made by rolling or extrusion and then machined into parts; bar stock and plate informally called billet).

2. Wikipedia, “Aluminium alloy”: en.wikipedia.org/wiki/Aluminium_alloy (cast alloys generally have lower tensile strengths than wrought alloys; 6000 series easy to machine and weldable, 6061 one of the most commonly used general-purpose alloys; 7000 series can be precipitation hardened to the highest strengths of any aluminium alloy).

3. A. Nourian-Avval and A. Fatemi, “Characterization and Analysis of Porosities in High Pressure Die Cast Aluminum by Using Metallography, X-Ray Radiography, and Micro-Computed Tomography”, Materials, 2020: pmc.ncbi.nlm.nih.gov/articles/PMC7412358 (casting defects can significantly reduce strength and ductility, and fatigue performance in particular; the paper studies die-cast aluminum).

4. Wikipedia, “6061 aluminium alloy”: en.wikipedia.org/wiki/6061_aluminium_alloy (remains resistant to corrosion even when the surface is abraded).

5. Wikipedia, “7075 aluminium alloy”: en.wikipedia.org/wiki/7075_aluminium_alloy (one of the most commonly used aluminium alloys for highly stressed structural applications; vulnerable to stress corrosion cracking; the T7 temper, equivalent to T73, reduces that susceptibility).

6. Aluminum Anodizers Council, “What is Anodizing?”: anodizing.org (anodizing is an electrochemical process that converts the metal surface into a decorative, durable, corrosion-resistant anodic oxide finish).