Free Engineering Tool
Surface Roughness Symbols Reference
ISO 1302 drawing symbol reference. Select a machining process or Ra value to see the proper drawing symbol, MRR indicator, and lay direction.
Symbol & Details
ISO 1302 Symbol Structure
The ISO 1302 surface texture symbol consists of a basic graphical symbol (check-mark shape) with annotations for Ra/Rz values, machining process, material removal, lay direction, and machining allowance.
Ra vs N Grade Cross-Reference
| Ra (μm) | N Grade | Typical Process | Application |
|---|---|---|---|
| 0.025 | N1 | Superfinish / Lapping | Gauge blocks, mirrors |
| 0.05 | N2 | Lapping | Precision gauges |
| 0.1 | N3 | Lapping / Honing | Bearing races, seals |
| 0.2 | N4 | Grinding / Honing | Crankshaft journals |
| 0.4 | N5 | Grinding | Bearing seats |
| 0.8 | N6 | Grinding / Fine turning | Mating surfaces |
| 1.6 | N7 | Turning / Milling | General machined parts |
| 3.2 | N8 | Turning / Milling | Non-critical surfaces |
| 6.3 | N9 | Rough machining | Internal surfaces |
| 12.5 | N10 | Rough turning / Sawing | Rough castings |
| 25 | N11 | Casting / Forging | Non-functional surfaces |
| 50 | N12 | Sand casting | As-cast surfaces |
Lay Direction Symbols
| Symbol | Meaning | Example |
|---|---|---|
| = | Parallel to projection plane | Turning, shaping |
| ⊥ | Perpendicular to projection plane | Cross-grinding |
| X | Crossed in two oblique directions | Honing |
| M | Multi-directional | Lapping, superfinishing |
| C | Approximately circular | Face turning |
| R | Approximately radial | Radial grinding |
| P | Non-directional, particulate | Shot blasting, EDM |
Ra (arithmetical mean roughness) is the most commonly used surface roughness parameter. It represents the average absolute deviation of the profile from the mean line, measured in micrometers (μm). Lower Ra values mean smoother surfaces.
MRR stands for Material Removal Required. The plain basic V-symbol means "any process allowed". A bar across the V means "machining required (material removal required)". A circle on the V means "no material removal allowed" (surface left as-produced).
Lay direction symbols indicate the predominant surface pattern direction:
- = Parallel to projection plane
- ⊥ Perpendicular
- X Crosshatch
- M Multi-directional
- C Circular
- R Radial
- P Non-directional/particulate
ISO 1302 defines how to indicate surface texture on technical drawings (symbols and notation). ISO 21920 defines the actual profile parameters (Ra, Rz, Rq, etc.) and their measurement methods. They are complementary standards.
Typical values: Ra 0.1–0.4 μm for bearing surfaces and seals; Ra 0.8–1.6 μm for mating/sliding surfaces; Ra 3.2–6.3 μm for general machined surfaces; Ra 12.5–25 μm for rough machining and castings.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional field balancing instruments and software. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
