What Is ISO 2768? A Complete Guide to CNC Machining Tolerance Standards

Quick Summary

• ISO 2768 is an international general tolerance standard that removes the need to mark every individual dimension on a drawing. It's split into Part 1 (linear and angular dimensions) and Part 2 (geometric tolerances).
• Part 1 defines four classes — f (fine), m (medium), c (coarse), v (very coarse). Part 2 (geometric tolerances) is rarely required in practice unless a part needs a precision fit.
• Specifying the fine (f) class for every dimension drives up machining cost and lead time, so it pays to apply tight tolerances only where they actually matter functionally.

Why Do CNC Drawings Need a Tolerance Standard?

The dimensions on a design drawing and the dimensions of the finished part can never match 100%. No matter what process is used, small deviations always occur — and a tolerance defines the range of deviation that won't cause assembly or functional problems.

For example, say you order 200 units of a Ø50mm shaft, and the measured values come back at Ø49.3–50.7mm (a ±0.7mm deviation from nominal). Whether that part is usable, or should be rejected and reworked, needs a clear standard to check against. Specifying a tolerance on the drawing — say, "passes at ±1.5mm (v-class), fails at ±0.3mm (m-class)" — removes the ambiguity.

This article covers:

• The two parts of ISO 2768 (linear/angular tolerances vs. geometric tolerances)
• Actual values for the f/m/c/v classes
• How to apply it on a drawing, and Creallo's own tolerance standard

What Is ISO 2768?

ISO 2768 is an internationally recognized general tolerance standard that removes the need to mark an individual tolerance on every dimension of a drawing.

The standard is made up of two parts:

• Part 1: General tolerances for linear and angular dimensions without individual tolerance indications. Four classes — f (fine), m (medium), c (coarse), v (very coarse).
• Part 2: Geometric tolerances (flatness, perpendicularity, symmetry, circular run-out, etc.) — rarely required in practice unless a part needs a precision fit.

Drawings typically use the Part 1 class on its own, e.g. "ISO 2768-m." This keeps the drawing clean without tolerancing every dimension individually.

That said, ISO 2768 is a set of general rules. If a specific dimension needs a tighter tolerance than the standard provides, it must be called out separately on the drawing. Always check whether a general tolerance class is noted in the title block, and whether any individual features carry their own callouts.

Why you shouldn't apply the fine (f) class to every dimension

Specifying the fine (f) class across the board requires more precise machining, higher-grade fixtures, and more skilled operators — and it raises the defect rate — so cost and lead time both increase. Keep tight tolerances only on dimensions that genuinely affect assembly or alignment, and leave the rest at a wider general tolerance. That's the more cost-effective way to design.

Part 1: General Tolerances for Linear and Angular Dimensions

Part 1 breaks tolerances into three categories: linear dimensions, external radii/chamfers, and angular dimensions. Most dimensions on a drawing fall into one of these three.

Table 1. Linear Dimension Tolerances (mm)

Use this table for ordinary linear dimensions — length, width, height. Radii and chamfers, which involve curvature, are governed by a separate table below.

Table 2. External Radii and Chamfer Tolerances (mm)

Angular dimensions use a different unit system than linear ones, so they're covered by their own table.

Table 3. Angular Dimension Tolerances (degrees, minutes)

Part 2: Geometric Tolerances

Part 2 doesn't work on an upper-limit/lower-limit basis. Instead, it defines an "allowed zone" — the actual surface has to fall between two reference planes or lines. In practice, this level of geometric tolerancing is rarely required outside of parts with precision fits — bearing housings, sealing surfaces, and similar. Most drawings only need Part 1 (linear tolerances). If your part does need geometric tolerancing, it's best handled through a direct conversation with our team.

How to Apply ISO 2768 on a Drawing

1. Define nominal dimensions on the 3D model.
2. Classify each feature by how critical it is to assembly and alignment (e.g., fastening hole positions → fine; rib wall thickness → coarse).
3. Assign f/m/c/v classes based on that criticality.
4. Add a callout like "ISO 2768-m" to the drawing's title block, and note individual tolerances only for the specific dimensions that need something tighter than the general standard.

Creallo's Tolerance Standard for CNC Machining

To make the four ISO 2768 classes (f/m/c/v) easier to apply in practice, Creallo simplifies them into two: general tolerance and precision tolerance. (General tolerance corresponds to ISO 2768's m class; precision tolerance corresponds to the f class.)

• Minimum tolerance we can hold: ±0.05mm
• Recommended default: ±0.1mm — unless a dimension genuinely needs to be tighter, we recommend designing to this value.
• If no tolerance is specified on the drawing, our general tolerance applies by default. If a dimension needs a precision tolerance, select the precision tolerance option under "Additional Options" at checkout and upload a 2D drawing along with it — our team will review it and follow up directly.

What Else to Check Alongside Tolerance in CNC Design

Getting tolerances right isn't the whole picture. If you don't also account for machinability (internal corners, undercuts, thin walls, etc.) and how finishing affects final dimensions, you can still end up with a part that doesn't match your design intent. For recommended undercut dimensions, fillet values, minimum wall thickness, and more, see our CNC design guide below.

• Related guide: CNC Design Guide and Key Considerations >>

Frequently Asked Questions

Q. What happens if ISO 2768 isn't specified on a drawing? 

Without a tolerance callout, different manufacturers may interpret dimensions using their own internal standards, which can lead to disputes. Referencing an internationally recognized standard like ISO 2768 gives both the buyer and the manufacturer a clear, shared baseline.

Q. Is GD&T different from ISO 2768? 

ISO 2768 Part 2 does cover geometric tolerancing concepts, but a more detailed system for form, orientation, and position tolerances is handled separately by GD&T (ASME Y14.5 and similar). Features with special functional requirements are often called out individually using GD&T symbols.

Q. Can I just apply the fine (f) class to every dimension? 

You can, but we don't recommend it. The fine class requires more precise fixturing and inspection, which drives up both machining cost and lead time. It's more efficient to keep tight tolerances only where they're functionally necessary and leave the rest at a wider class.

Need CNC Parts Made to Precise Tolerances? Creallo Can Help

Creallo lets you upload a drawing and get an automatic, real-time review of tolerance, geometry, and machining difficulty through our AI-powered DFM analysis — with results you can check right away. If a dimension needs a precision tolerance, select that option under "Additional Options" and attach a 2D drawing — our team will review it and follow up with guidance.

From design to product. Fast and accurate.

Once you've confirmed your tolerance classes, upload your drawing and get a CNC machining quote today.

Related link:

• Precision CNC Machining Services >>