Tolerance Query

Quick online query of ISO standard tolerances for shafts and holes.

Type:

Shaft

Hole

Size

Range: 0 - 3150

Tolerance Range

Upper deviation

Lower deviation

Maximum

Minimum

What is dimensional tolerance?

Size tolerance in manufacturing and engineering refers to the permissible limit or limits of variation in the physical dimensions of a part. Essentially, it's the degree to which the size of a component can vary but still be considered acceptable for its intended application. Tolerances are crucial for ensuring that parts fit and function properly, especially in complex assemblies.

- Definition -

Size tolerance is defined as the difference between the upper and lower permissible sizes of a part or component. This range determines how much a part can deviate from the standard or nominal size while still being acceptable.

- Choosing Tolerance -

The selection of appropriate tolerances depends on many factors, including the intended use of the part, manufacturing capabilities, and cost considerations. Tighter tolerances are typically required for high-precision applications, like aerospace components, whereas looser tolerances might be acceptable for less critical applications.

Representation of tolerance zone

According to the international standard ISO 286, the tolerance zone consists of tolerance grade and deviation position.

- Tolerance Class -

Indicates the size of the variable range, which is divided into 20 levels, IT01, IT00, IT1, IT2, IT3,..., IT18. The smaller the number, the smaller the variable range.

- Deviation Position -

Used to indicate the offset between the variable range and the basic size, it is composed of 28 English marks. The 26 English letters have removed i, l, o, q, w, and added cd, ef, fg, js, za, zb, zc. Holes are represented by capital letters, and shafts are represented by lowercase letters. The relative positions are roughly as shown below:

FAQ

What is the difference between shaft and hole tolerances?
Shaft tolerances use lowercase letters (a, b, c, ..., z) and typically have negative deviations (smaller than nominal). Hole tolerances use uppercase letters (A, B, C, ..., Z) and typically have positive deviations (larger than nominal). This system ensures proper fits when shafts and holes are paired.
How do I read the tolerance zone notation like "h7" or "H6"?
The letter indicates the deviation position (h/H = fundamental deviation of zero), and the number indicates the tolerance grade (precision level). For example, "h7" means a shaft with zero fundamental deviation and IT7 tolerance grade. Smaller numbers mean tighter tolerances.
What does "fundamental deviation" mean in tolerance calculations?
Fundamental deviation is the deviation closest to the zero line (nominal size). For holes, it's usually the lower deviation; for shafts, it's usually the upper deviation. This determines the position of the tolerance zone relative to the nominal size.
Why are there so many different tolerance positions (a-z, A-Z)?
Different positions create different fit types when paired. Positions closer to the zero line (f, g, h for shafts; F, G, H for holes) create tighter fits, while positions farther away create looser fits. This system allows engineers to specify exact fit characteristics for different applications.
How do I choose the right tolerance grade for my application?
Consider the function, manufacturing cost, and precision requirements. IT6-IT7 for precision applications (bearings, gauges), IT8-IT9 for general machining, IT10-IT11 for rough machining, and IT12+ for casting or rough operations. Tighter tolerances cost more to achieve.
What happens if I exceed the size range (0-3150mm)?
This calculator covers the standard ISO 286 range for most engineering applications. For larger sizes, tolerances become proportionally larger, but the calculation principles remain the same. Special applications may require custom tolerance calculations or non-standard approaches.