Anodizing is a key finishing process for aluminum, enhancing corrosion resistance, durability, and appearance.
To simplify communication across the industry, standardized nomenclature and designations are used to describe different anodizing methods, film thicknesses, sealing treatments, and intended performance levels.
Anodizing standards are not created in isolation—they are maintained and validated by key organizations across the metals industry.
ASTM International publishes widely used standards for anodic coatings, while the American National Standards Institute ensures those standards are nationally recognized and developed through accredited processes.
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The Aluminum Association supports the industry with alloy designation systems and technical resources that align with anodizing practices. Together, these organizations help ensure that anodizing nomenclature and performance designations are consistent, reliable, and globally recognized.
The tables below outline the common anodizing codes and their meanings, providing engineers, designers, and buyers with a clear reference when specifying aluminum products for projects that require consistent quality and finish.
Alfiniti, Inc. is the largest aluminum manufacturer in North America.
Anodizing Terminology and Military Standards
There is a common industry terminology for anodizing in commercial applications which grew out of Alcoa’s trademarked Alumilite designations. There is also a military specification that covers anodizing that is commonly used – MIL-A-8625.
Mechanical Finishes
(“*” denotes the ones we offer)
- A1 – Preliminary grinding and polishing prior to anodizing
- A2 – Buff directly on as-fabricated (mill finish) surface
- *B – Polish finish (round tube only)
- *C1 – Polish finish, No. 180-220 emery
- C2 – Satin finish, hand rubbed with steel wool
- C3 – Satin finish, compound or brushed backed sander
- *D – Polish finish, No. 140-180 emery
- *E – Polish finish, No. 120-140 emery
- G1 – Very fine sand blast
- G2 – Fine blast G3 Medium blast
- G4 – Coarse blast
- H1 – Fine shot blast
- H2 – Medium shot blast
- H3 – Coarse shot blast
- *K – Wire brush finish
- M – Burnished finish
- N – Sand burnished finish
Chemical Finishes to prepare the surface before the anodic coating is applied
(“*” denotes the ones we offer)
- *R1 – Caustic etch
- *R2 – Caustic etch for diffuse reflectors
- R3 – Sulfuric-chromic acid etch
- R4 – Bright dip (nitric-hydrofluoric)
- *R5 – Bright dip (nitric-phosphoric)
Anodizing Coating Thickness and Comparative Designations (Alcoa Alumilite System)
| Film Thickness | Alcoa Designation | Aluminum Association Designations |
Descriptions | Type of Finish |
|---|---|---|---|---|
| 0.0001 | Alumilite 200 .00015 minimum film thickness |
A21 | Clear (natural) coating | Protective and decorative (coating less than 0.4 mils thick) (Thickness to be specified by customer) |
| 0.0002 | Alumilite 201 .0002 minimum film thickness |
A22 | Coating with integral color | |
| 0.0003 |
Alumilite 202 .0003 minimum film thickness Alumilite 203 .00036 minimum film thickness |
A23 A2X |
Coating with impregnated color Other |
|
| 0.0004 0.0005 0.0006 |
Alumilite 204 .0004 minimum film thickness |
A31 A32 A33 A3X |
Other | Architectural Class II (0.4 to 0.7 mil coating) |
| 0.0007 | Alumilite 214 .0007 minimum film thickness |
A31 A32 A33 A3X |
Other | Architectural Class I (0.7 mil and greater anodic coating) |
| up |
A41 A42 A43 A4X |
Other |
Now the military designation from MIL-A-8625 – the entire specification is public domain and is included as an attachment in this section. Please check latest revisions.
1.1 Scope.
This specification covers the requirements for six types and two classes of electrolytically formed anodic coatings on aluminum and aluminum alloys for non-architectural applications (see 6.1).
1.2 Classification.
Anodic coating Types and Classes covered by this specification are as specified herein (see 6.2 and 6.21):
1.2.1 Types
Type I – Chromic acid anodizing, conventional coatings produced from chromic acid bath, (see 3.4.1)
Type IB – Chromic acid anodizing, low voltage process, 22 +/- 2V, (see 3.4.1)
Type IC – Non-chromic acid anodizing, for use as a non-chromate alternative for Type I and IB coatings (see 3.4.1 and 6.1.2)
Type II – Sulfuric acid anodizing, conventional coatings produced from sulfuric acid bath, (see 3.4.2)
Type IIB – Thin sulfuric acid anodizing, for use as a non-chromate alternative for Type I and IB coatings (see 3.4.2 and 6.1.2)
Type III – Hard Anodic Coatings (see 3.4.3)
1.2.2 Classes.
Class 1 – Non-dyed (see 3.5.)
Class 2 – Dyed (see 3.6.)
Why it matters:
Clear anodizing designations give engineers, buyers, and fabricators a common language. By using standardized terms, you can specify coating thickness, finish type, and performance expectations without ambiguity, ensuring everyone involved understands exactly what’s required.
These standards also connect directly to performance in the field. The right anodizing designation helps ensure aluminum products meet durability, corrosion resistance, and appearance needs for their intended application—whether in architectural projects, industrial machinery, or consumer products.
Finally, referencing widely recognized systems such as Alcoa’s Alumilite designations, MIL-A-8625, ASTM, and Aluminum Association standards builds confidence. It means your anodized aluminum will be consistent, compliant, and reliable, no matter the source or scale of production.
Alfiniti can help:
Our team can guide you through these trade-offs, ensuring that you choose the alloy best suited for your application. Whether your priority is strength, corrosion resistance, manufacturability, or cost, we’ll match you with tubing that meets ASTM B221 specifications and your project requirements.
Need to know about aluminum alloy products?
Check out our Aluminum Mill Specifications by Alloys page for a list of all of the alloy products and their key characteristics.
