Interference & Clearance Fit Calculator

A clearance fit always has a gap between the shaft and hole, allowing free movement. An interference fit (press fit) always has overlap, requiring force to assemble. A transition fit can result in either a slight clearance or slight interference, depending on where each part falls within its tolerance range. Use clearance fits for rotating parts, interference fits for permanent joints, and transition fits for accurate location.

H7/g6 is a fit designation per ISO 286. The letter indicates the fundamental deviation (position of the tolerance zone relative to nominal). The number indicates the IT grade (width of the tolerance zone). H7 means the hole has a fundamental deviation of zero (starts at nominal) with IT grade 7. g6 means the shaft is slightly below nominal with IT grade 6. Together, H7/g6 creates a sliding clearance fit.

H7/h6 is the most commonly specified fit. It gives a close sliding fit with minimal clearance. H7/g6 is popular for bearings and sliding fits. H7/p6 and H7/s6 are common interference fits for press-fit pins and dowels. The right fit depends on whether the parts need to slide, locate precisely, or be permanently joined.

ISO 286 is the international standard for limits and fits using the hole-basis or shaft-basis system with letter-number designations like H7/g6. ANSI B4.1 is the American standard that uses RC, LC, LT, LN, and FN class designations. Both systems achieve the same goal but use different notation. ISO 286 is more widely used globally.

Hole-basis fits (capital H for the hole) are the most common because it is easier and cheaper to adjust shaft size than to ream or bore a hole to a specific size. Use shaft-basis fits when you have a standard shaft size (like ground rod stock) and want to adjust the hole. Most engineering drawings and this calculator use the hole-basis system.