ENGINEERING REFERENCE · PHYSICAL PLAQUE SELECTION
A VDI number narrows the finish conversation. A physical reference and a molded sample help your team approve the result before the tool is committed.
Compare adjacent grades under the same lighting, then confirm the selected appearance in the production resin, color, and part geometry.
Explore all 12 VDI 3400 grades
| Grade | Indicative Ra (µm) | Selection band |
|---|---|---|
| VDI 12 | 0.40 µm | Fine |
| VDI 15 | 0.56 µm | Fine |
| VDI 18 | 0.80 µm | Fine-to-matte |
| VDI 21 | 1.12 µm | Mid-range |
| VDI 24 | 1.60 µm | Mid-range |
| VDI 27 | 2.24 µm | Mid-range |
| VDI 30 | 3.15 µm | Coarse |
| VDI 33 | 4.50 µm | Coarse |
| VDI 36 | 6.30 µm | Coarse |
| VDI 39 | 9.00 µm | Heavy texture |
| VDI 42 | 12.5 µm | Heavy texture |
| VDI 45 | 18.0 µm | Heavy texture |
Measurement note: This Ra figure matches the widely published Charmilles/Agie-derived VDI 3400 comparison chart, cross-checked here against an independent EDM reference-standard supplier's published specification (see citations below), not only against this site's own material. It is an indicative comparison value, not a licensed-standard quotation, gloss measurement, texture-depth conversion, guaranteed molded appearance, or contractual tolerance. If another document (for example a downloadable PDF) shows a different rounded figure, treat this page as the controlling reference until confirmed otherwise with your supplier.
Why compare a physical texture plaque?
A screen image cannot reliably communicate touch, directional reflection, or how a finish will appear on a particular polymer and color. The site’s physical plaques support side-by-side selection; they do not replace production-resin trials, a licensed standard, or an agreed inspection method.
What to specify before mold approval
- The grade and exact surfaces that receive the finish
- The physical master plaque and its material
- Production resin, color, and representative molded sample
- Inspection method, locations, and acceptance criteria
- Draft and release review for the actual part geometry
Review physical reference plaques Back to vdi3400.com
Technical references
- VDI official catalog entry for VDI 3400 — describes the guideline as covering electrical discharge machining terminology, processes, and applications.
- Xometry surface-finish guide — an industry comparison source; values are not a substitute for the controlling project specification.
This guide is a supplier-published selection aid. It is not issued, approved, or certified by VDI. Confirm any contractual requirement against the licensed reference and your approved production sample.
Content last reviewed: 2026-09-24.