Toprecision — Precision Fastening & Connection Solutions

Anodizing is electrochemically grown oxide: half the layer builds outward, half converts base metal. On a threaded part, that dual movement is the whole story.

Bottom line: for most Surface Treatment applications the decision comes down to load, environment and assembly method — the Surface Treatment guide walks through the selection.

The dimensional arithmetic

A 10 µm anodic layer raises external dimensions by 10 µm but consumes 10 µm of base metal — so a thread's pitch diameter grows by only the outward half, roughly half the coating spec. Still, on precision threads even 5 µm matters: M3 tolerances leave less than 50 µm total play.

Type II vs Type III

• Type II (decorative, 8–15 µm): standard for consumer products; threads usually need no masking at common class limits.
• Type III (hard anodizing, 25–50+ µm): abrasion resistance for aerospace and industrial tools, but dimensional growth demands masked threads or post-coating machining.

Practical specification advice

Call out masking for threads on Type III, specify dye color explicitly (blacks vary widely), and re-verify friction: anodized surfaces are abrasive and change torque-preload conversion — K-factor rises noticeably. Topprecision anodizes its aluminum fastener line in-house-controlled partner processes with thread-masking standard on precision sizes, and supplies friction data per finish class.

Fastener material comparison

Need help selecting the right fastener material?

Toprecision cold-heads and CNC-turns fasteners in steel (4.6–12.9), stainless 304/316/410, aluminum 6061/7075, titanium Grade 5 and engineering plastics. Send the service environment and load requirement — we will recommend the material and grade with tensile test data. Request material selection support.