What does the circle in a surface finish symbol mean?

Material removal is prohibited — the surface must not be machined. It appears on castings and forgings where the as-formed surface is to be preserved. Machining such a surface is a nonconformance even if the resulting finish would be smoother.

What does a number in a surface finish symbol mean?

Its upper limit of Ra in micrometres unless another parameter is named. A callout of 1.6 means 1.6 µm Ra or smoother. It is a maximum, not a nominal value, and not a target to aim at.

What does a number in parentheses mean on a finish callout?

It is a reference value only and creates no requirement. It typically records what a comparable surface achieved in production. A shop is not obliged to meet a parenthesised figure, and an inspector should not reject on it.

How do I specify a ground finish on a drawing?

Write the process name on the long leg of the symbol, with the roughness value above the V. Specifying the method rather than only the finish is used where the process itself matters — grinding leaves a different residual stress and surface integrity from turning at the same Ra.

What are the lay symbols?

They describe the direction of the predominant surface pattern: parallel, perpendicular, crossed, multidirectional, circular, radial and particulate. Lay matters where the texture direction affects function — a shaft seal, for example, performs differently with a circumferential versus an axial lay.

Surface Texture Symbols

Eleven elements that make up a surface texture callout, and which of them state a requirement rather than a preference.

Data verified 2026-09-29 · based on ISO 1302:2002

Find a symbol

Surface Texture Symbol Elements (ISO 1302)

Element^[2]	How it appears^[2]	What it means^[2]	Notes^[2]
Basic symbol #	✓ (two legs only)	A surface is indicated but no method is specified	The bare symbol is rarely used alone — it is the base onto which the other marks are added.
Material removal prohibited #	✓ with a circle in the V	The surface must NOT be machined	Used on castings and forgings where the surface is to be left as-formed. A finishing operation would violate it.
Material removal required #	✓ with a bar across the V	The surface must be machined	The default interpretation where removal is intended. Machine marks are acceptable and expected.
Material removal — any method #	✓ with a bar and no other mark	Machining required, method not specified	The shop chooses the process. Used where the finish matters but how it is achieved does not.
Ra value #	Number above the V	Upper limit of Ra in micrometres	A single number is an upper limit. A number in parentheses means it is a reference, not a requirement.
Rz value #	Number after Rz	Parameter must be named where it is not Ra	Without a parameter letter the number is read as Ra. Where another parameter is intended it must be written.
Upper and lower limit #	Two numbers	Maximum and minimum roughness	Both limits specified. Rare — generally a maximum is enough, and a minimum adds cost without benefit.
Machining method #	Text on the long leg	The process to be used	Written as a process name such as 'ground' or 'turned'. Method specification is used where the process itself matters, not just the finish.
Lay direction #	Symbol on the long leg	The direction of the predominant surface pattern	Lay symbols: = parallel, ⊥ perpendicular, X crossed, M multidirectional, C circular, R radial, P particulate.
Sampling length #	Text in the upper-left	Cut-off length, typically 0.8 mm	Where omitted, the default cut-off from the standard applies. Specifying it matters where the surface has long-wavelength waviness.
All-round #	Circle at the junction of the legs	The requirement applies to all surfaces around the part	Same convention as the all-round weld symbol — the circle modifies the symbol rather than the surface.

A single roughness number is an upper limit, not a nominal value. Writing "1.6" on a surface means the surface must be 1.6 µm Ra or smoother — it does not mean the shop should aim at 1.6 and may produce anything near it. That is the opposite of how linear dimensions work, and it is the most common misreading of a finish callout.

Two other conventions matter. A number in parentheses is reference only — it records what a comparable surface achieved and creates no requirement, so a shop is not obliged to meet it. And where the parameter is not Ra it must be named: a bare number is always read as Ra, so Rz, Rmax or Rq all need their letter written.

The prohibition symbol is worth understanding properly. When a drawing says material removal is prohibited, machining the surface is a nonconformance even if the result would be better — the intent is that the cast or forged skin is preserved for its properties, not that a particular finish is required.

Specifying Finish Without Over-Specifying It

Surface finish is one of the easiest places to add cost for no benefit. Three habits keep it under control.

Put the callout only where it is needed. A blanket roughness note covering the whole drawing tightens every surface on the part, including the ones nobody touches. The same requirement written on the three functional surfaces costs a fraction of that.

Specify a maximum only. Two-sided roughness limits are occasionally justified — a surface that must be rough enough to grip, for instance — but they are rare. In most cases a minimum limit only adds inspection work.

Choose the coarsest finish that works. Going from Ra 3.2 to Ra 1.6 typically costs a finishing pass; going from 1.6 to 0.4 typically means grinding instead of turning. The functional difference between 0.4 and 0.8 is rarely worth the process change.

Where a surface's function depends on peaks rather than on average roughness — sealing, fatigue initiation, coating adhesion — specify Rz rather than Ra, because Ra can stay low while isolated peaks remain high. That is a case where the extra parameter earns its place.

Frequently Asked Questions

What does the circle in a surface finish symbol mean?: Material removal is prohibited — the surface must not be machined. It appears on castings and forgings where the as-formed surface is to be preserved. Machining such a surface is a nonconformance even if the resulting finish would be smoother.
What does a number in a surface finish symbol mean?: Its upper limit of Ra in micrometres unless another parameter is named. A callout of 1.6 means 1.6 µm Ra or smoother. It is a maximum, not a nominal value, and not a target to aim at.
What does a number in parentheses mean on a finish callout?: It is a reference value only and creates no requirement. It typically records what a comparable surface achieved in production. A shop is not obliged to meet a parenthesised figure, and an inspector should not reject on it.
How do I specify a ground finish on a drawing?: Write the process name on the long leg of the symbol, with the roughness value above the V. Specifying the method rather than only the finish is used where the process itself matters — grinding leaves a different residual stress and surface integrity from turning at the same Ra.
What are the lay symbols?: They describe the direction of the predominant surface pattern: parallel, perpendicular, crossed, multidirectional, circular, radial and particulate. Lay matters where the texture direction affects function — a shaft seal, for example, performs differently with a circumferential versus an axial lay.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	ASME B46.1 — Surface Texture (Surface Roughness, Waviness and Lay)	standard	ASME B46.1-2019
[2]	ISO 1302 — Indication of surface texture in technical product documentation	standard	ISO 1302:2002
[3]	ISO 4287 — Surface texture: Profile method	standard	ISO 4287:1997

Data Sources

Standard	Revision	What it covers on this page
ISO 1302 — Indication of surface texture in technical product documentation	ISO 1302:2002	the symbol construction and every element listed
ASME B46.1 — Surface Texture	ASME B46.1-2019	the American practice, which differs in symbol layout
ISO 4287 — Surface texture: Profile method	ISO 4287:1997	the parameter definitions the callouts refer to

Cross-checked against:

Every symbol element checked against the ISO 1302 construction rules
The single-number-as-upper-limit convention verified — it is the most commonly misread element
The parenthesised-value convention cross-checked against ISO 1302 rather than assumed from practice

ISO and ASME symbol conventions differ in layout and in some parameter defaults. A drawing should state which standard applies; where it does not, the title block or the drawing's origin usually indicates it.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "Surface Texture Symbols." https://refmanual.com/charts/surface-texture-symbols/ (accessed 2026-09-29). Data from ISO 1302 — Indication of surface texture in technical product documentation, ISO 1302:2002.

BibTeX

@misc{surface-texture-symbols,
  title        = {Surface Texture Symbols},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/surface-texture-symbols/}},
  note         = {Accessed: 2026-09-29},
  source       = {ISO 1302 — Indication of surface texture in technical product documentation, ISO 1302:2002}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Surface Texture Symbols
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/surface-texture-symbols/
PY  - 2026
DA  - 2026-09-29
N1  - Source: ISO 1302 — Indication of surface texture in technical product documentation, ISO 1302:2002
ER  -

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