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What Bike Parts Work Asks of an Anodizing Shop

September 25, 2026

Bicycle components are consumer products that happen to be machined. That single fact is what makes them different from the industrial work most anodizing shops run, and it is where finishers new to the segment get caught out.

The two bars you have to clear

Functional. Corrosion resistance and wear, same as any part.

Cosmetic. The part is on a bike, at eye level, next to three other parts from the same brand. It has to match them. A rider will notice a shade difference that an industrial customer would never look for.

Clearing the first is routine. Clearing the second, repeatably, batch after batch, is what gets you kept.

Dimensional control is tighter than it looks

Machinists working on bike parts hold bearing seats to single hundredths of a millimeter. Your coating grows about half its thickness outward from the original surface, so a diameter moves by roughly the full coating thickness.

Run the numbers on a typical case. A 28 mm bearing seat cut for a light press fit, with perhaps 0.010 mm of interference designed in. Give it 40 microns of hard anodize and the seat has moved 0.040 mm, four times the whole fit. The bearing will not go in, or it goes in crushed.

What that means for you:

• Get the masking instruction in writing before the parts arrive, not after somebody notices
• Hold the thickness range you quoted. The machinist set their allowance around your number
• Say when you cannot mask something cleanly. A plug that shifts is worse than a plug that was never promised
• Ask what the feature is. “Mask bore A” is an instruction. “That bore takes a 6902 bearing” tells you how much it matters

The alloy problem, and how to talk about it

6061 and 7075 do not take dye the same way. Zinc and copper in 7075 change how the oxide grows and how it holds dye, so the same bath gives a darker, often greyer or greener result.

Bike brands hit this constantly, because stems are usually 6061 and cranks and chainrings are usually 7075, and they want them to match.

You cannot fix it in the bath. What you can do is be the finisher who explains it before the batch rather than after:

1. Tell them the two alloys will differ, and roughly how
2. Suggest a dark shade, where the difference is least visible
3. Offer separate tuned baths per alloy with a stated tolerance on the match
4. Say plainly when a requested match is not achievable

That conversation, had early, is worth more to a brand than a discount.

Master samples are the whole quality system

Approve a physical sample, keep one, let the customer keep one, and judge every subsequent batch against it under agreed lighting.

Without a master there is no shared definition of correct, and every discussion becomes two people describing a color from memory. Dye baths deplete, mill lots vary, rack position changes thickness. A master sample is how you catch drift while it is still one rack.

For a brand that sells four colors across six parts, a shop that maintains master samples is not a vendor, it is infrastructure.

Batch economics and small runs

Most bike parts orders are 25 to 500 pieces. The brands know that racking 25 collars costs close to what racking 200 costs, and they will ask whether several parts can share one batch.

Say yes where you can, and say what the constraints are. A stem, a seat collar and a set of spacers in one black, on one rack, is a normal request and an easy yes. Three different colors in one week is a different conversation.

The shops that handle this well quote a rack rather than a piece, and explain it.

The fatigue conversation

Anodizing reduces the fatigue life of aluminum, and thicker coatings reduce it more. Published testing on 7075-T6 cranks under European protocols found cycles to failure falling as anodized depth rose.

This matters because stems, cranks and steerer clamps carry a rider, and some of them get fatigue tested to ISO 4210 or EN 15194.

Two things follow:

• If a customer asks for hard anodize on a fatigue critical part, it is worth one sentence asking whether they have tested it that way. You will occasionally save somebody a failed test, and they will remember.
• If a part is going for testing, the sample has to be finished exactly as production will be. Same type, same thickness, same masking. A test passed on a differently finished sample is not a test of the shipping part.

What to put in front of a machine shop

Shops looking for a finishing partner for bike work want four answers, quickly:

They ask	What a good answer sounds like
Turnaround	“Seven working days from receipt, in writing”
Thickness	“Type II at 15 to 20 microns, held and measured”
Color match	“Yes across batches on one alloy, with an approved master. Across 6061 and 7075, expect a visible difference and here is what we can do”
Small batches	“Rack minimum is X, and we will combine parts in one color”

A finisher who gives those four answers in a first email wins the relationship. One who says “send us the parts and we will see” does not.

If you finish aluminum and want work from machine shops making bike components, register as a vendor. Free to list, and the shops come to you.

Frequently asked questions

Keep reading

• What Bike Parts Machinists Want From a Metal Supplier
• Testing Bike Components: What Brands Actually Need