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Surface Finishes & Coatings Specifications

Ra reference, anodizing, plating, powder coat, ENP, passivation, and 8+ more finishes.

Assorted color swatches in green, white, black, orange, and teal arranged as overlapping rectangular bars.
Surface Roughness (Ra) Reference ▾
Technical diagram of surface finish tolerances with labels A–F, showing maximum waviness height/spacing, roughness values, machining allowance, lay symbol, and an example on a surface block.
Ra (μm) Description Process Application
0.1–0.4 Mirror polish Lapping Optical, gauges
0.8–1.6 Fine machined Precision grind Mating surfaces
1.6–3.2 Standard Turning, milling Most common
3.2–6.3 Coarse Rough mill Non-critical
6.3+ Very rough Sawing Hidden

Surface Roughness (Ra) Reference

Common surface finish specifications and their applications

Ra Value (μm) Ra Value (μin) Finish Description Typical Process Applications
0.025 – 0.05 1 – 2 Super fine polish Lapping, superfinishing Optical surfaces, gage blocks
0.1 – 0.2 4 – 8 Fine polish Fine grinding, polishing Bearing surfaces, seals
0.4 – 0.8 16 – 32 Fine machined Precision grinding, fine turning Mating surfaces, hydraulic cylinders
1.6 – 3.2 63 – 125 Standard machined Turning, milling, boring General machined parts (most common)
6.3 – 12.5 250 – 500 Coarse machined Rough turning, drilling Non-critical surfaces, clearance
25 – 50 1000 – 2000 Very rough Sawing, flame cutting, as-cast Hidden surfaces, raw stock

Quick Reference:

Ra 3.2μm (125μin): Standard CNC finish, cosmetic acceptable

Ra 1.6μm (63μin): Fine finish, good for O-ring seals

Ra 0.8μm (32μin): Precision finish, adds cost

Ra 0.4μm (16μin): Ground finish, expensive

Aluminum Anodizing (Mil-PRF-8625 Type I, II, and III) ▾
  • Type I: 0.00001″–0.0001″. Clear. $$. 7–14 days.
  • Type II: 0.0002″–0.001″. Wide colors. $–$$. 5–10 days.
  • Type III (Hard): 0.001″–0.003″. 60–70 Rc. $$$. 7–14 days.
  • Growth ~50% of thickness. Different alloys won’t color match.

Type I (Chromic Acid)

  • Thickness: 0.00002" – 0.0001" (0.5-2.5µm)
  • Colors: Gray/tan (minimal dye uptake)
  • Very thin, minimal dimensional change
  • Cost: $
  • Lead time: 7-14 days
  • Best for: Aerospace, tight tolerances, weldments

Type II (Sulfuric Acid)

  • Thickness: 0.0002" – 0.001" (5-25µm)
  • Colors: Clear, black, red, blue, gold, etc.
  • Hardness: ~400 HV
  • Cost: $ – $$
  • Lead time: 5-10 days
  • Best for: Aesthetic parts, corrosion protection

Type III (Hard Coat)

  • Thickness: 0.001" – 0.004" (25-100µm)
  • Colors: Natural gray to black (limited color)
  • Hardness: ~600 HV (very hard)
  • Cost: $$ – $$$
  • Lead time: 7-14 days
  • Best for: Wear resistance, extreme environments
Powder Coating ▾
  • 2–6 mils. Cure 350–400°F. RAL/Pantone. No VOCs.
  • May pool in corners. Cost $–$$. 5–10 days.
Electroplating (Chrome, Nickel, Zinc) ▾
Plating Thickness Notes
Chrome 0.00002"–0.0005" Decorative or hard
Nickel 0.0002"–0.002" Solderable
Zinc 0.0002"–0.001" Sacrificial protection
Other Finishes ▾
  • ENP: Uniform on complex geometry. $$–$$$. 7–14 days.
  • Passivation: SS only. ASTM A967. $. 5–7 days.
  • Bead Blast: Matte finish. Ra 1–6μm. $. 1–3 days.
  • Black Oxide: Steel. <0.00001″ change. $. 3–7 days.
  • Cerakote: Ceramic coating. $$$$. 7–14 days.
  • Tumbling: Deburring. $. 3–7 days.
Cost & Lead Time Comparison ▾
Finish Cost Lead Time Best For
As Machined $ 0 days Non-critical
Bead Blast $ 1–3 days Matte
Passivation $ 5–7 days SS corrosion
Anodize II $–$$ 5–10 days AL color
Powder Coat $–$$ 5–10 days Durable color
ENP $$–$$$ 7–14 days Uniform wear
Anodize III $$–$$$ 7–14 days Hard wear
Chrome $$$+ 10–21 days Dec./hard

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