ISO 2768 is an international standard that defines general tolerances for linear and angular dimensions on engineering drawings. Part 1 (ISO 2768-1) covers linear and angular tolerances in four classes: f (fine), m (medium), c (coarse), and v (very coarse). It eliminates the need to specify individual tolerances on every dimension.

When should I use general tolerances?

General tolerances apply to all dimensions on a drawing that do not have individual tolerances specified. They are suitable for features produced by standard machining operations where normal workshop accuracy is sufficient. For critical fits, mating surfaces, or precision features, specific tolerances should be applied.

What is the difference between f, m, c, and v tolerance classes?

The four classes represent increasing levels of permissible deviation: f (fine) has the tightest tolerances, m (medium) is the most commonly used for general machining, c (coarse) is for rough machining or non-critical parts, and v (very coarse) is for castings and flame-cut parts.

How are angular tolerances applied in ISO 2768-1?

Angular tolerances depend on the shorter side of the angle. For example, if the shorter side is ≤10 mm, the angular tolerance for class m is ±1°. As the shorter side increases, the angular tolerance decreases. This is defined in Table 2 of ISO 2768-1.

How do I note ISO 2768-1 on a drawing?

The standard is referenced in the drawing title block as 'ISO 2768-m' (for medium class) or 'ISO 2768-fH' when combined with Part 2 (geometrical tolerances). Simply write the standard designation followed by the tolerance class letter.

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一般公差計算器 — ISO 2768-1

依公差等級與公稱尺寸查詢 ISO 2768-1 的一般公差值。包含線性與角度公差及完整參考表格。

ISO 2768-1 線性公差角度公差

結果

線性公差

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公差等級

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尺寸範圍

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上限

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下限

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角度公差（較短邊）

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表 1 — 線性尺寸（允許偏差，單位 mm）

範圍 (mm)	f (精確)	m (中等)	c (粗糙)	v (極粗糙)
0.5 – 3	±0.05	±0.1	±0.2	—
3 – 6	±0.05	±0.1	±0.3	±0.5
6 – 30	±0.1	±0.2	±0.5	±1
30 – 120	±0.15	±0.3	±0.8	±1.5
120 – 400	±0.2	±0.5	±1.2	±2.5
400 – 1000	±0.3	±0.8	±2	±4
1000 – 2000	±0.5	±1.2	±3	±6
2000 – 4000	—	±2	±4	±8

表 2 — 角度尺寸（允許偏差）

較短邊 (mm)	f (精確)	m (中等)	c (粗糙)	v (極粗糙)
≤ 10	±1°	±1°	±1°30′	±3°
10 – 50	±0°30′	±0°30′	±1°	±2°
50 – 120	±0°20′	±0°20′	±0°30′	±1°
120 – 400	±0°10′	±0°10′	±0°15′	±0°30′
> 400	±0°5′	±0°5′	±0°10′	±0°20′

ℹ️ 注意： ISO 2768-1 適用於圖面上未指定個別公差的所有尺寸。公差等級字母置於標題欄中，例如「ISO 2768-m」。

什麼是通用公差？

依據 ISO 2768-1 的通用公差，定義了圖面上未標註個別公差的線性與角度尺寸之允許偏差。它們代表了使用標準加工工藝可達到的常規車間精度。

實際尺寸必須落在以下範圍內：

公差等級選擇

f (精確) — 精密加工，緊密配合。需要嚴格的工藝控制。
m (中等) — 最常用。標準加工（車削、銑削、鑽孔）。
c (粗糙) — 粗加工、焊接結構、非關鍵零件。
v (極粗糙) — 鑄件、火焰切割零件、鍛件。

圖面標註

範例 — 標題欄標註

僅限線性公差： ISO 2768-m

與幾何公差（ISO 2768-2）結合： ISO 2768-mK

這表示：線性公差等級「m」+ 幾何公差等級「K」。

⚠️ 重要： 通用公差不適用於具有個別公差的尺寸、參考尺寸（括號內）或受其他標準規範的尺寸。