LIMITS, FITS AND TOLERANCES CALCULATOR (ISO SYSTEM)

Limits, fits and tolerances calculator is developed to work in line with ISO 286-1 (2010), ISO 286-2 (2010) and ANSI B4.2 (1978) standards which are based on metric units. According to input parameters of nominal size and hole/ shaft tolerances, size limits and deviations for hole/shaft are calculated and fit type is selected among the clearance, transition and interference fits. The schematic representation of the fit is also drawn. The preferred fits advised by ISO and ANSI standards can be found in the Supplement section.

The tolerances defined in ISO 286-1 (2010) are applicable to size range from 0 mm to 3150 mm but there are a lot of exceptional cases defined in the standard which depend on tolerance selection. If the calculation results given by the calculator are "---", then this means that input parameters are not applicable according to ISO standard.

Limits and tolerances for shaft & hole fit

Calculator:

INPUT PARAMETERS
Parameter Value Unit
Nominal Size mm
Hole Tolerance ---
Shaft Tolerance ---
 


Note : Use dot "." as decimal separator.


RESULTS
HOLE
Parameter Value Unit
Designation --- ---
Hole Upper Deviation ---  μm(0.001mm)
Hole Lower Deviation --- μm(0.001mm)
Maximum Hole Size --- mm
Minimum Hole Size --- mm
SHAFT
Parameter Value Unit
Designation --- ---
Shaft Upper Deviation ---  μm(0.001mm)
Shaft Lower Deviation ---  μm(0.001mm)
Maximum Shaft Size --- mm
Minimum Shaft Size --- mm
FIT
Parameter Value Unit
Designation --- ---
Fit Type --- ---
Maximum Clearance --- μm(0.001mm)
Minimum Clearance --- μm(0.001mm)



Definitions:

Nominal size: Size of a feature of perfect form as defined by the technical drawing.

Deviation: The difference between a size and the corresponding nominal size.

Upper deviation: The difference between the maximum limiting size and the corresponding nominal size of a feature.

Lower deviation: The difference between the minimum limiting size and the corresponding nominal size of a feature.

Tolerance: The difference between the maximum and minimum size limits of a part.

Clearance Fit: A fit type where clearance exists between assembled parts under all tolerance conditions.

Interference Fit: A fit type where interference exists between assembled parts under all tolerance conditions.

Transition Fit: A fit type where clearance or interference can exist between assembled parts depending on tolerance conditions.

Precision Measurement Tools:

This section is prepared to give brief idea about the devices that can be used for the measurement of the inside diameter of the hole and outside diameter of a shaft. Slide calipers (Digital, Dial or Vernier), outside/ inside micrometers, bore gauges and pin gauges are often used for diameter measurement and control in mechanical engineering applications. The selection of the tool depends on the accuracy requirement and the feature to be measured.

Slide Calipers: A tool used to measure the inside and outside distance (diameter) and depth of a feature. Different models exist such as digital, dial and vernier calipers. Measurement accuracy of a slide caliper generally ranges from +/- 0.001 inch to +/- 0.0015 inch (+/- 0.02 mm to +/- 0.04 mm). These values depend on the quality of caliper and measurement length. Different measuring length options exist but common one is 0 to 6 inches (0 – 150 mm).

Micrometers: An accurate measurement device to measure dimensions of an object. It’s also known as micrometer screw gage since there is a calibrated screw exist inside the micrometer. Main types are outside, inside and depth micrometers. Outside micrometers are used to measure diameter and thickness of shafts, wires, plates. Inside micrometers are used to measure diameter of holes. Depth micrometers are used to measure the depths of holes, slots, shoulders. Measurement accuracy of micrometers is in the range +/- 0.00005 inch to +/- 0.001 inch (+/- 0.001 mm  to +/- 0.02 mm). The accuracy value depends on the micrometer type, quality of and the measurement range.

Bore Gauge: A bore gauge is a tool to measure the bore diameter of a cylinders, pipes and bearings. There are different types of bore gauges which can be classified as dial bore gauges and transfer bore gauges. Transfer bore gauges consists of telescopic gauge and small hole gauges. In transfer type bore gauges, there is no scale on the tool. After the measurement with a transfer type bore gauge, the distance between contacts of the gauge are measured with a caliper or micrometer. In case of dial bore gauge, the measurement is read from the dial during the measurement. Different measurement length options exist.

Pin Gauges: These tools are used to check the hole size if it’s in the limits of size. Pin gauges are precision machined metal plugs and there are different tolerance classes such as Class ZZ, Z, X and XX. Pins can be either “plus” or “minus” tolerance pins. “Minus” gauge pins are most commonly used. GO/NOGO measurement shall be done with pin gauges to check upper and lower limits of the hole.

Supplements:

Link Usage
Preferred fits advised by ISO and ANSI standard Preferred fits advised by ISO 286-1 (2010) and ANSI B4.2 (1978) standard are given to help user about the selection of fit. Whenever possible, selection of tolerance class shall be done among these tolerances to avoid too many numbers of tools and gauges.
Interference (press & shrink) fit calculator The calculator which calculates press fit force, required temperatures for shrink fit, fit stresses and other parameters necessary for interference fit design

Reference:
  • IS0 286-1 (2010) Geometrical product specifications (GPS) - ISO code system for tolerances on linear sizes - Part 1: Basis of tolerances, deviations and fits
  • IS0 286-2 (2010) Geometrical product specifications (GPS) - ISO code system for tolerances on linear sizes - Part 2: Tables of standard tolerance classes and limit deviations for holes and shafts
  • ANSI/ASME B4.2 (1978) Preferred Metric Limits and Fits