Tolerance Query

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: