Worked example
A bore of Ø20 with limits 20.000 and 20.021 and a shaft with limits 19.980 and 19.993: minimum clearance = 20.000 − 19.993 = 0.007 mm, maximum clearance = 20.021 − 19.980 = 0.041 mm. The minimum is positive, so every pair fits with play: a clearance fit, with between 7 and 41 µm of it. These are the values preset above.
The three kinds of fit
- Clearance fit: the shaft is always smaller than the hole – for parts that must move or be assembled by hand.
- Interference fit (press fit): the shaft is always larger – the parts are pressed or shrunk together and transmit load by friction.
- Transition fit: sometimes play, sometimes interference, depending on where the actual sizes fall – for parts that must locate precisely but can be separated.
For what the letters and numbers of an ISO fit like H7/g6 mean, see ISO 286 tolerance classes and fits. To add up a whole chain of parts, use the tolerance stack-up calculator.
Frequently asked questions
How do I calculate clearance between a hole and a shaft?
Minimum clearance = hole minimum − shaft maximum; maximum clearance = hole maximum − shaft minimum. A hole of 20.000/20.021 and a shaft of 19.980/19.993 give 0.007 to 0.041 mm.
How do I know if a fit is clearance, transition or interference?
If the minimum clearance is zero or more, it is a clearance fit. If the maximum is zero or less, it is an interference fit. In between it is a transition fit.
What does negative clearance mean?
Interference: the shaft is larger than the hole by that amount, so the parts have to be pressed or shrunk together.
Can I use this for H7/g6?
Yes, if you enter the hole and shaft limits for that fit from the drawing or the ISO 286 tables. The calculator does not look up the limits itself.
More free machinist calculators
- Inch to mm – Convert inches to millimetres and back, fractions like 1 3/8 included. Exact factor 25.4, with a chart of every 1/64 inch.
- RPM and feed – Calculate spindle RPM from surface speed and diameter, surface speed from RPM, and feed rate from chip load – metric and imperial, with formulas.
- Taper – Taper ratio, half angle and taper per foot from the large and small diameter and the length, or the small diameter from the angle.
- Bolt circle – X and Y coordinates of evenly spaced holes on a bolt circle, with the hole spacing, start angle and centre offset. Copy the table into your program.
- Sine bar – Gauge block height for a sine bar angle, or the angle from a known stack, for 5 in, 10 in, 100 mm, 200 mm or any other bar length.
- Metal removal rate – Metal removal rate in cm³/min or in³/min from depth, width and feed – milling and turning, metric and imperial, with the formulas.
- Drill point depth – Length of a drill's point cone from diameter and point angle, and the total depth needed for a full-diameter hole to depth.
- Right triangle – Hypotenuse and angles from two legs, or the legs from the hypotenuse and an angle – for chamfers, dovetails, tapers and hole positions.
- Machining time – Cutting time from length, feed and spindle speed – turning with feed per revolution, milling with feed rate and number of passes.
- Decimal to fraction – Turn a decimal inch or a millimetre value into the nearest fraction – 8ths to 128ths – with the error in millimetres.
- Degrees to DMS – Convert decimal degrees to degrees, minutes and seconds and back, with the angle in radians.
- SFM to m/min – Convert surface feet per minute to metres per minute and back, and inches per minute to mm per minute, with the exact factors.
- TPI to pitch – Convert a thread pitch in millimetres to threads per inch (TPI) and back, for matching metric and inch threads.
- Cpk calculator – Paste measurements from Excel, enter USL and LSL and get Cp, Cpk, Pp and Ppk. Says plainly when 25 values are too few for an index.
- Tolerance stack-up – Add up the tolerances of a chain of parts: closing gap, worst case and statistical RSS for up to eight dimensions. Free, in your browser.
- Chip thinning – Feed per tooth to program when the radial width of cut is below half the cutter diameter, so the real chip thickness stays right.
- Ball-nose stepover – Scallop height left by a ball-nose cutter from the stepover, or the stepover for a wanted scallop height, on a flat surface.
- Surface finish – Theoretical Rt and estimated Ra of a turned surface from the feed per revolution and the tool nose radius.
- Torque and power – Torque from power and speed in newton-metres or pound-feet, and power from torque and speed. The formulas with worked examples.
- Spur gear – Pitch and outside diameter, centre distance, ratio and circular pitch of a pair of external spur gears from the module and the tooth numbers.
Making parts for a customer who wants paperwork?
Automotive and aerospace customers ask for proof that the parts match the drawing. See first article inspection (FAI), PPAP explained and the true position calculator.