The ISO 286 standard, titled "Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes," is the international reference for linear tolerances used in engineering and manufacturing. It provides a standardized system for defining the limits and fits of machined parts, specifically for cylindrical features (holes and shafts) and parallel surfaces (slots and keys). Structure of the Standard The standard is divided into two primary parts:
This is the reference size from which the limits are derived. For example, a 30mm shaft and a 30mm hole share a basic size of 30mm. iso 286 pdf
Fundamental Deviation: Identified by a letter (uppercase for holes, lowercase for shafts), this determines the position of the tolerance zone relative to the nominal (basic) size. For H7 (50mm): Lower = 0
To use the data found in an ISO 286 PDF effectively, one must understand three core concepts: Basic Size, Tolerance Grade, and Fundamental Deviation. the minimum clearance is 0.009 mm.
