Ano
Article · Specifications
What Does MIL-A-8625 Type II Class 2 Mean?
It calls for Sulfuric Acid Anodizing that takes dye, most commonly black. Type II is the process, Class 2 means dyed, and the drawing should also name the color because Class 2 alone does not distinguish black from gold.
Breaking the Callout Apart
MIL-A-8625 is the specification governing anodic coatings on aluminum. You may also see it as MIL-PRF-8625, which is the same document after a change of category, or with a revision letter such as MIL-A-8625F.
Type II names the process: Sulfuric Acid Anodizing, the general purpose workhorse that most machined aluminum receives. The alternatives in the specification are Type I, chromic acid, which we do not run, and Type III, Hard Coat.
Class 2 means the coating is dyed. Class 1 is non-dyed and comes out clear to a light matte gray. Class 2 covers black and every color in the dye range.
What the Callout Is Usually Missing
Color. Class 2 tells a shop the part is dyed but not what shade, and a clear part delivered against a drawing that meant black is scrap for its purpose even though nothing was done incorrectly. Name the color explicitly.
The second omission is a coating allowance on close-tolerance features. Type II builds less than Hard Coat, but on a gauged thread or a precision bore it still matters. The third is which features stay bare, if any.
What a Complete Version Looks Like
A callout that will not come back as a question reads something like: ANODIZE PER MIL-A-8625 TYPE II CLASS 2, COLOR BLACK. MASK THREADS PER DRAWING. DIMENSIONS APPLY AFTER ANODIZE.
That version names the specification, the type, the class and the color, tells the shop which features stay bare, and settles whether the dimensions on the page are before or after finishing. Five pieces of information, one extra line, and none of the usual questions.
Compare it with the version we receive most often, which is ANODIZE PER MIL-A-8625 TYPE II CLASS 2 and nothing else. That is a legitimate callout and we can run it, but it does not say what color, so we ask, and asking costs a day.
What We Do With It
We run this combination every working day. If the callout is complete we quote from it and put the date on the quote. If the color is missing, or the tolerances look tight with no allowance stated, we raise it before the parts go in a tank rather than after.
Every type and class combination on both MIL-A-8625 and MIL-DTL-5541 is laid out in the callout decoder.
Common Questions
Is MIL-A-8625 the Same as MIL-PRF-8625?
Yes. The document was recategorized, which changed the prefix. A drawing citing either is asking for the same thing, and older drawings commonly still say MIL-A-8625.
What Is the Difference Between Class 1 and Class 2?
Class 1 is non-dyed and Class 2 is dyed. The class rides on either type, so a black Hard Coat part is Type III Class 2 and a clear anodized part is Type II Class 1.
Does Type II Class 2 Have to Be Black?
No. Class 2 means dyed, and black is simply the most common choice. We run red, blue, gold, green, orange and brown as well, plus custom matching. The drawing should name the color.
Does the Drawing Need to State a Thickness?
Not always, but it should on anything with a fit, a gauged thread or a close-tolerance bore. Where a thickness is stated we run to it; where it is not, we run to the normal range for the type and flag anything that looks tight.
Do You Run MIL-A-8625 Type I?
No. When a drawing carries a Type I chromic acid callout we say so before quoting instead of substituting Type II and hoping the difference stays buried until inspection.
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Have a Part That Needs Finishing?
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