Fits – Inch (ANSI B4.1)
RC, LC, LT, LN and FN fit classes with their limits, standard tolerance grades, modified fits, and worked examples.
ANSI/ASME B4.1, Preferred Limits and Fits for Cylindrical Parts, is the American inch standard for how tight or loose a shaft and hole should be. It names 34 ready-made classes in five families (RC, LC, LT, LN and FN), each with the limits of size for the hole and the shaft in every size range, so there is nothing to calculate: pick the class, read the limits. This page gives the classes, the standard tolerance grades behind them, and the limits of every class for two common size ranges, taken from the Machinery’s Handbook. It is part of the Fits & Tolerances guide; the metric equivalent is Fits – Metric (ISO System).
A note on the standard. The Handbook (31st edition) lists the standard as ANSI/ASME B4.1-1967, reaffirmed 2009, and marks it “out of print”. It is still published and used. The recommendations agree with the American-British-Canadian (ABC) conferences for sizes up to 20 inches, with further experimental work above that. All tables below are in thousandths of an inch (0.001 in), as in the standard.
The classes
| Family | Letters | Classes | What they are |
|---|---|---|---|
| Running and sliding fits | RC | RC 1 to RC 9 | Clearance fits for parts that move. The clearance grows with the size and with the class number |
| Locational clearance fits | LC | LC 1 to LC 11 | Clearance fits for parts that are normally stationary but can be freely assembled and disassembled |
| Locational transition fits | LT | LT 1 to LT 6 | A compromise between clearance and interference, for accurate location |
| Locational interference fits | LN | LN 1 to LN 3 | For rigidity and alignment, without bore-pressure requirements and not to carry load by friction |
| Force or shrink fits | FN | FN 1 to FN 5 | Interference fits with a nearly constant bore pressure across sizes |
The Handbook describes the classes as follows. The numbers in a class designation always run from tighter to looser or from lighter to heavier.
| Class | Description (Handbook) |
|---|---|
| RC 1 close sliding | Accurate location of parts that must assemble without perceptible play |
| RC 2 sliding | Accurate location, with greater maximum clearance than RC 1. Parts move and turn easily but are not intended to run freely; in larger sizes they may seize with small temperature changes |
| RC 3 precision running | About the closest fits that can be expected to run freely, for precision work at slow speeds and light journal pressures; not suitable where appreciable temperature differences are likely |
| RC 4 close running | Chiefly for running fits on accurate machinery with moderate surface speeds and journal pressures, where accurate location and minimum play are desired |
| RC 5, RC 6 medium running | Higher running speeds, or heavy journal pressures, or both |
| RC 7 free running | Where accuracy is not essential, or where large temperature variations are likely, or both |
| RC 8, RC 9 loose running | Where wide commercial tolerances may be necessary, together with an allowance, on the external member |
| LC locational clearance | Normally stationary parts that can be freely assembled or disassembled: from snug fits for parts needing accuracy of location, through medium clearance fits for parts such as spigots, to the looser fastener fits where freedom of assembly is of prime importance |
| LT locational transition | Accuracy of location is important, but either a small amount of clearance or interference is permissible |
| LN locational interference | Accuracy of location is of prime importance, and parts need rigidity and alignment, with no special bore-pressure requirements. Not for parts meant to carry friction loads: that is FN |
| FN 1 light drive | Light assembly pressure, giving more or less permanent assemblies; suitable for thin sections or long fits, or in cast-iron external members |
| FN 2 medium drive | Ordinary steel parts, or shrink fits on light sections: about the tightest fits that can be used with high-grade cast-iron external members |
| FN 3 heavy drive | Heavier steel parts, or shrink fits in medium sections |
| FN 4, FN 5 force | Parts that can be highly stressed, or shrink fits where the heavy pressing forces required are impractical |
Standard tolerance grades
Every class is built from standard tolerance grades, which set the width of the hole and shaft tolerances (Table 6 in the Handbook). The classes use grades 4 to 13. A larger grade number means a looser tolerance; each size range has its own value, so a large part is allowed more variation than a small one. Values in thousandths of an inch:
| Nominal size (in) | Grade 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
|---|---|---|---|---|---|---|---|---|---|---|
| 0 – 0.12 | 0.12 | 0.15 | 0.25 | 0.4 | 0.6 | 1 | 1.6 | 2.5 | 4 | 6 |
| 0.12 – 0.24 | 0.15 | 0.2 | 0.3 | 0.5 | 0.7 | 1.2 | 1.8 | 3 | 5 | 7 |
| 0.24 – 0.40 | 0.15 | 0.25 | 0.4 | 0.6 | 0.9 | 1.4 | 2.2 | 3.5 | 6 | 9 |
| 0.40 – 0.71 | 0.2 | 0.3 | 0.4 | 0.7 | 1 | 1.6 | 2.8 | 4 | 7 | 10 |
| 0.71 – 1.19 | 0.25 | 0.4 | 0.5 | 0.8 | 1.2 | 2 | 3.5 | 5 | 8 | 12 |
| 1.19 – 1.97 | 0.3 | 0.4 | 0.6 | 1 | 1.6 | 2.5 | 4 | 6 | 10 | 16 |
| 1.97 – 3.15 | 0.3 | 0.5 | 0.7 | 1.2 | 1.8 | 3 | 4.5 | 7 | 12 | 18 |
| 3.15 – 4.73 | 0.4 | 0.6 | 0.9 | 1.4 | 2.2 | 3.5 | 5 | 9 | 14 | 22 |
| 4.73 – 7.09 | 0.5 | 0.7 | 1 | 1.6 | 2.5 | 4 | 6 | 10 | 16 | 25 |
| 7.09 – 9.85 | 0.6 | 0.8 | 1.2 | 1.8 | 2.8 | 4.5 | 7 | 12 | 18 | 28 |
| 9.85 – 12.41 | 0.6 | 0.9 | 1.2 | 2 | 3 | 5 | 8 | 12 | 20 | 30 |
| 12.41 – 15.75 | 0.7 | 1 | 1.4 | 2.2 | 3.5 | 6 | 9 | 14 | 22 | 35 |
| 15.75 – 19.69 | 0.8 | 1 | 1.6 | 2.5 | 4 | 6 | 10 | 16 | 25 | 40 |
Example: a 2-inch size (the 1.97 to 3.15 row) has a grade 6 tolerance of 0.7 thousandths (0.0007 in) and a grade 9 tolerance of 3.0 thousandths (0.003 in). The tolerance on the hole is called H and the tolerance on the shaft is a lower-case letter (such as f or g) plus a grade number; these “ABC symbols” are listed for each class below.
Running and sliding fits (RC)
The clearance columns give the smallest and largest clearance. The limits are added to or subtracted from the basic size (a + or − sign shows which); the hole limits are upper / lower, the shaft limits are upper / lower. The class RC 9 hole and shaft have no letter designation in the standard.
RC fits: 0.71 to 1.19 in
| Class | Hole / shaft | Type | Clearance (0.001 in) | Hole limits | Shaft limits |
|---|---|---|---|---|---|
| RC 1 | H5 / g4 | Close sliding | 0.3 to 0.95 | +0.4 / 0 | −0.3 / −0.55 |
| RC 2 | H6 / g5 | Sliding | 0.3 to 1.2 | +0.5 / 0 | −0.3 / −0.7 |
| RC 3 | H7 / f6 | Precision running | 0.8 to 2.1 | +0.8 / 0 | −0.8 / −1.3 |
| RC 4 | H8 / f7 | Close running | 0.8 to 2.8 | +1.2 / 0 | −0.8 / −1.6 |
| RC 5 | H8 / e7 | Medium running | 1.6 to 3.6 | +1.2 / 0 | −1.6 / −2.4 |
| RC 6 | H9 / e8 | Medium running | 1.6 to 4.8 | +2 / 0 | −1.6 / −2.8 |
| RC 7 | H9 / d8 | Free running | 2.5 to 5.7 | +2 / 0 | −2.5 / −3.7 |
| RC 8 | H10 / c9 | Loose running | 4.5 to 10 | +3.5 / 0 | −4.5 / −6.5 |
| RC 9 | H11 / – | Loose running | 7 to 15.5 | +5 / 0 | −7 / −10.5 |
RC fits: 1.97 to 3.15 in
| Class | Hole / shaft | Type | Clearance (0.001 in) | Hole limits | Shaft limits |
|---|---|---|---|---|---|
| RC 1 | H5 / g4 | Close sliding | 0.4 to 1.2 | +0.5 / 0 | −0.4 / −0.7 |
| RC 2 | H6 / g5 | Sliding | 0.4 to 1.6 | +0.7 / 0 | −0.4 / −0.9 |
| RC 3 | H7 / f6 | Precision running | 1.2 to 3.1 | +1.2 / 0 | −1.2 / −1.9 |
| RC 4 | H8 / f7 | Close running | 1.2 to 4.2 | +1.8 / 0 | −1.2 / −2.4 |
| RC 5 | H8 / e7 | Medium running | 2.5 to 5.5 | +1.8 / 0 | −2.5 / −3.7 |
| RC 6 | H9 / e8 | Medium running | 2.5 to 7.3 | +3 / 0 | −2.5 / −4.3 |
| RC 7 | H9 / d8 | Free running | 4 to 8.8 | +3 / 0 | −4 / −5.8 |
| RC 8 | H10 / c9 | Loose running | 6 to 13.5 | +4.5 / 0 | −6 / −9 |
| RC 9 | H11 / – | Loose running | 9 to 20.5 | +7 / 0 | −9 / −13.5 |
Locational fits (LC, LT, LN)
Locational clearance (LC)
Several LC classes (LC 1 to LC 4) have a minimum clearance of zero: the largest shaft is the same size as the smallest hole, so the parts just touch at the tightest end.
LC fits: 0.71 to 1.19 in
| Class | Hole / shaft | Type | Clearance (0.001 in) | Hole limits | Shaft limits |
|---|---|---|---|---|---|
| LC 1 | H6 / h5 | Locational clearance | 0 to 0.9 | +0.5 / 0 | 0 / −0.4 |
| LC 2 | H7 / h6 | Locational clearance | 0 to 1.3 | +0.8 / 0 | 0 / −0.5 |
| LC 3 | H8 / h7 | Locational clearance | 0 to 2 | +1.2 / 0 | 0 / −0.8 |
| LC 4 | H10 / h9 | Locational clearance | 0 to 5.5 | +3.5 / 0 | 0 / −2 |
| LC 5 | H7 / g6 | Locational clearance | 0.3 to 1.6 | +0.8 / 0 | −0.3 / −0.8 |
| LC 6 | H9 / f8 | Locational clearance | 0.8 to 4 | +2 / 0 | −0.8 / −2 |
| LC 7 | H10 / e9 | Locational clearance | 1.6 to 7.1 | +3.5 / 0 | −1.6 / −3.6 |
| LC 8 | H10 / d9 | Locational clearance | 2 to 8 | +3.5 / 0 | −2 / −4.5 |
| LC 9 | H11 / c10 | Locational clearance | 4.5 to 13 | +5 / 0 | −4.5 / −8 |
| LC 10 | H12 / – | Locational clearance | 7 to 23 | +8 / 0 | −7 / −15 |
| LC 11 | H13 / – | Locational clearance | 10 to 34 | +12 / 0 | −10 / −22 |
LC fits: 1.97 to 3.15 in
| Class | Hole / shaft | Type | Clearance (0.001 in) | Hole limits | Shaft limits |
|---|---|---|---|---|---|
| LC 1 | H6 / h5 | Locational clearance | 0 to 1.2 | +0.7 / 0 | 0 / −0.5 |
| LC 2 | H7 / h6 | Locational clearance | 0 to 1.9 | +1.2 / 0 | 0 / −0.7 |
| LC 3 | H8 / h7 | Locational clearance | 0 to 3 | +1.8 / 0 | 0 / −1.2 |
| LC 4 | H10 / h9 | Locational clearance | 0 to 7.5 | +4.5 / 0 | 0 / −3 |
| LC 5 | H7 / g6 | Locational clearance | 0.4 to 2.3 | +1.2 / 0 | −0.4 / −1.1 |
| LC 6 | H9 / f8 | Locational clearance | 1.2 to 6 | +3 / 0 | −1.2 / −3 |
| LC 7 | H10 / e9 | Locational clearance | 2.5 to 10 | +4.5 / 0 | −2.5 / −5.5 |
| LC 8 | H10 / d9 | Locational clearance | 4 to 11.5 | +4.5 / 0 | −4 / −7 |
| LC 9 | H11 / c10 | Locational clearance | 6 to 17.5 | +7 / 0 | −6 / −10.5 |
| LC 10 | H12 / – | Locational clearance | 10 to 34 | +12 / 0 | −10 / −22 |
| LC 11 | H13 / – | Locational clearance | 14 to 50 | +18 / 0 | −14 / −32 |
Locational transition (LT)
The “fit” column gives the maximum interference (a minus sign) and the maximum clearance (plus), the two ends of the fit.
LT fits: 0.71 to 1.19 in
| Class | Hole / shaft | Type | Fit: interference to clearance | Hole limits | Shaft limits |
|---|---|---|---|---|---|
| LT 1 | H7 / js6 | Locational transition | −0.25 to +1.05 | +0.8 / 0 | +0.25 / −0.25 |
| LT 2 | H8 / js7 | Locational transition | −0.4 to +1.6 | +1.2 / 0 | +0.4 / −0.4 |
| LT 3 | H7 / k6 | Locational transition | −0.6 to +0.7 | +0.8 / 0 | +0.6 / +0.1 |
| LT 4 | H8 / k7 | Locational transition | −0.9 to +1.1 | +1.2 / 0 | +0.9 / +0.1 |
| LT 5 | H7 / n6 | Locational transition | −1.1 to +0.2 | +0.8 / 0 | +1.1 / +0.6 |
| LT 6 | H7 / n7 | Locational transition | −1.4 to +0.2 | +0.8 / 0 | +1.4 / +0.6 |
LT fits: 1.97 to 3.15 in
| Class | Hole / shaft | Type | Fit: interference to clearance | Hole limits | Shaft limits |
|---|---|---|---|---|---|
| LT 1 | H7 / js6 | Locational transition | −0.3 to +1.5 | +1.2 / 0 | +0.3 / −0.3 |
| LT 2 | H8 / js7 | Locational transition | −0.6 to +2.4 | +1.8 / 0 | +0.6 / −0.6 |
| LT 3 | H7 / k6 | Locational transition | −0.8 to +1.1 | +1.2 / 0 | +0.8 / +0.1 |
| LT 4 | H8 / k7 | Locational transition | −1.3 to +1.7 | +1.8 / 0 | +1.3 / +0.1 |
| LT 5 | H7 / n6 | Locational transition | −1.5 to +0.4 | +1.2 / 0 | +1.5 / +0.8 |
| LT 6 | H7 / n7 | Locational transition | −2 to +0.4 | +1.2 / 0 | +2 / +0.8 |
Locational interference (LN)
The columns give the smallest and largest interference.
LN fits: 0.71 to 1.19 in
| Class | Hole / shaft | Type | Interference (0.001 in) | Hole limits | Shaft limits |
|---|---|---|---|---|---|
| LN 1 | H6 / n5 | Locational interference | 0 to 1 | +0.5 / 0 | +1 / +0.5 |
| LN 2 | H7 / p6 | Locational interference | 0 to 1.3 | +0.8 / 0 | +1.3 / +0.8 |
| LN 3 | H7 / r6 | Locational interference | 0.4 to 1.7 | +0.8 / 0 | +1.7 / +1.2 |
LN fits: 1.97 to 3.15 in
| Class | Hole / shaft | Type | Interference (0.001 in) | Hole limits | Shaft limits |
|---|---|---|---|---|---|
| LN 1 | H6 / n5 | Locational interference | 0.1 to 1.3 | +0.7 / 0 | +1.3 / +0.8 |
| LN 2 | H7 / p6 | Locational interference | 0.2 to 2.1 | +1.2 / 0 | +2.1 / +1.4 |
| LN 3 | H7 / r6 | Locational interference | 0.4 to 2.3 | +1.2 / 0 | +2.3 / +1.6 |
Force and shrink fits (FN)
The columns give the smallest and largest interference. FN classes use finer size ranges than the other families (for example 0.95 to 1.19 and 1.97 to 2.56 in). FN 1 has no shaft letter in the table, and FN 3 does not start until about 0.95 in. The interference varies almost directly with diameter, which keeps the bore pressure nearly constant across sizes, and the spread between smallest and largest is kept small to hold the pressure within reasonable limits.
FN fits: 0.95 to 1.19 in
| Class | Hole / shaft | Type | Interference (0.001 in) | Hole limits | Shaft limits |
|---|---|---|---|---|---|
| FN 1 | H6 / – | Light drive | 0.2 to 1.1 | +0.5 / 0 | +1.1 / +0.7 |
| FN 2 | H7 / s6 | Medium drive | 0.6 to 1.9 | +0.8 / 0 | +1.9 / +1.4 |
| FN 3 | H7 / t6 | Heavy drive | 0.8 to 2.1 | +0.8 / 0 | +2.1 / +1.6 |
| FN 4 | H7 / u6 | Force | 1 to 2.3 | +0.8 / 0 | +2.3 / +1.8 |
| FN 5 | H8 / x7 | Force | 1.3 to 3.3 | +1.2 / 0 | +3.3 / +2.5 |
FN fits: 1.97 to 2.56 in
| Class | Hole / shaft | Type | Interference (0.001 in) | Hole limits | Shaft limits |
|---|---|---|---|---|---|
| FN 1 | H6 / – | Light drive | 0.6 to 1.8 | +0.7 / 0 | +1.8 / +1.3 |
| FN 2 | H7 / s6 | Medium drive | 0.8 to 2.7 | +1.2 / 0 | +2.7 / +2 |
| FN 3 | H7 / t6 | Heavy drive | 1.3 to 3.2 | +1.2 / 0 | +3.2 / +2.5 |
| FN 4 | H7 / u6 | Force | 2.3 to 4.2 | +1.2 / 0 | +4.2 / +3.5 |
| FN 5 | H8 / x7 | Force | 3.2 to 6.2 | +1.8 / 0 | +6.2 / +5 |
Using the tables
- Find the size range that contains your basic size (a size on a boundary belongs to the lower range).
- Read the class row: the hole limits and shaft limits are added to the basic size, using the sign shown.
- Check the fit. Smallest clearance = smallest hole − largest shaft; largest clearance = largest hole − smallest shaft. These agree with the clearance columns printed in the tables.
- Dimension it. Put the limits on the drawing (hole 2.0000 to 2.0005, shaft 1.9993 to 1.9996) or give the class and the basic size and let the shop look up the limits, as long as the standard is named on the drawing.
- Other sizes and classes. The Handbook (and the standard) give every class for every size range up to 19.69 in; the ABC agreements cover that range, and the standard itself goes further.
Modified fits: B and S
Sometimes holes and shafts of other sizes than the standard ones have to be produced, but the same clearance or interference must be kept. The standard allows two modifications, both of which give nonstandard parts with the same limits of clearance or interference:
| Symbol | System | What changes | Example |
|---|---|---|---|
| B (e.g. LC 4B) | Bilateral hole | The hole tolerance becomes bilateral (plus and minus): useful where the hole is made by a fixed tool such as a drill or reamer and a longer wear life is wanted | LC 4B |
| S (e.g. LC 4S) | Basic shaft | The maximum size of the shaft is the basic size (as in the basic shaft system); the hole limits are shifted by the same amount | LC 4S |
The Handbook’s rule for the bilateral hole: the hole tolerance is changed so that the plus limit is that of the next finer grade (from Table 6), and the minus limit equals the amount by which the plus limit was lowered. The shaft limits are lowered by that same amount. The limits of clearance are identical.
Worked examples
Example 1: the Handbook’s Class RC 1 fit at 2 inches
A Class RC 1 fit is to be used for a mating hole and shaft of 2-inch nominal size, where accurate location with no perceptible play is needed. For the 1.97 to 3.15 in range, Table 8a gives clearance 0.4 to 1.2, hole H5 +0.5 / 0, shaft g4 −0.4 / −0.7 (thousandths of an inch).
- Maximum hole = 2 + 0.0005 = 2.0005; minimum hole = 2.0000.
- Maximum shaft = 2 − 0.0004 = 1.9996; minimum shaft = 2 − 0.0007 = 1.9993.
- Minimum clearance = 2.0000 − 1.9996 = 0.0004 in; maximum clearance = 2.0005 − 1.9993 = 0.0012 in.
Example 2: choosing between LC 2 and LC 5 for a 1 inch spigot
A 1-inch spigot must locate a cover (0.71 to 1.19 in range) and be freely assembled by hand.
| Class | Clearance (0.001 in) | Comment |
|---|---|---|
| LC 2 H7/h6 | 0 to 1.3 | Snug: can touch at the tight end (zero clearance); best location |
| LC 5 H7/g6 | 0.3 to 1.6 | Always some clearance (0.0003 in at least): easier assembly, a little more play |
If the cover must always slip on by hand, choose LC 5 (minimum clearance 0.0003 in). If location matters more and an occasional light touch is acceptable, choose LC 2.
Example 3: a bilateral hole (LC 4B at 6 inches)
LC 4 at 6 inches (range 4.73 to 7.09) is hole +6.0 / 0 (grade 10), shaft 0 / −4.0 (grade 9), clearance 0 to 10.0. For LC 4B the Handbook gives hole +4.0 / −2.0 and shaft −2.0 / −6.0.
- The next finer grade (9) in Table 6 for that range is 4.0 thousandths, so the plus limit becomes +4.0.
- The plus limit was lowered by 6.0 − 4.0 = 2.0, so the minus limit is −2.0 (hole +4.0 / −2.0).
- The shaft is lowered by the same 2.0: 0 / −4.0 becomes −2.0 / −6.0.
- Check the clearance: smallest = −2.0 − (−2.0) = 0; largest = +4.0 − (−6.0) = 10.0. The same as LC 4.
Example 4: an FN 2 drive fit at 2 inches
For the 1.97 to 2.56 in range, FN 2 (H7 / s6) gives hole +1.2 / 0 and shaft +2.7 / +2 thousandths: an interference of 0.8 to 2.7 thousandths (0.0008 to 0.0027 in).
- Smallest interference = 2.0000 + 0.0020 − 2.0012 = 0.0008 in.
- Largest interference = 2.0027 − 2.0000 = 0.0027 in.
- Per inch of diameter this is 0.0004 to 0.00135 in/in, which fits the Handbook’s statement that forced fits usually need 0.001 to 0.0025 in per inch. How much force and stress it creates is on the Press, Shrink and Expansion Fits page.
Troubleshooting
| Symptom | Likely cause | Try |
|---|---|---|
| An RC 1 or RC 2 fit seizes in larger sizes | The clearance is only a few ten-thousandths of an inch; a small temperature change closes it | Use RC 3 or RC 4, or control temperature, finish and cleanliness |
| LC 1 to LC 4 parts bind at the tight end | Zero minimum clearance: the parts can touch | Use LC 5 (always some clearance) or tighten the process |
| An LT fit assembles by hand one day and needs a press the next | That is what a transition fit does; the parts fall anywhere in a range from clearance to interference | Use LN for always-tight, or LC for always-loose |
| A shrunk part cracks or loosens | Too much or too little interference for the hub thickness and material | Check hub stress; see the press fit page; use a lower FN class in cast iron or thin hubs |
| A modified fit does not match the table | B or S was applied to the wrong part, or the finer grade was taken from the wrong size range | Use the Handbook’s rule: same clearance limits, hole one grade finer and bilateral (B) |
Related
- Fits & Tolerances: the overview and quick reference.
- How Fits Work: clearance, transition and interference.
- Fits – Metric (ISO System): the ISO equivalent.
- Press, Shrink and Expansion Fits: the physics of FN fits.
- Tolerances by Process and Surface Finish: which process holds which tolerance grade.
FAQ
Why are there so many classes?
To give a design a choice of how loose or tight the fit is, in even steps, with each class applying across all sizes. The classes in each family are steps along one scale: RC 1 to RC 9 from tightest to loosest, FN 1 to FN 5 from lightest to heaviest.
Can I mix a hole from one class with a shaft from another?
Only if you recompute the fit. The class limits come as a pair. Mixing gives a fit that is not in the standard; calculate it from the limits.
What does “out of print” mean for ANSI B4.1?
The Handbook notes that the 1967 edition (reaffirmed 2009) was no longer in print at the time of publication but still available for reference. Many drawings still cite it; use it as written on the drawing.
Where are the tables for other sizes?
In the Handbook (Tables 8a to 12 cover sizes up to 19.69 inches) and in the standard, which also gives sizes above that. This page shows two size ranges as examples.
Is RC 1 the same as H7/g6?
It is close in spirit, but the two systems differ. RC 1 has H5/g4 grades and a tighter fit range than metric H7/g6. Do not swap them without recalculating the limits.
How do I convert between inch classes and ISO fits?
You cannot convert by name. Convert the basic size to millimeters, then pick the ISO fit with the clearance you need, using the metric page. See also ANSI B4.2.
References
- Machinery’s Handbook, 31st edition, Industrial Press: “ANSI/ASME Standard Limits and Fits” (definitions; factors affecting selection of fits; Table 6, standard tolerances; Tables 8a to 12, running and sliding, clearance locational, transition locational, force and shrink and interference locational fits; “Modified Standard Fits”).
- ANSI/ASME B4.1-1967 (R2009), Preferred Limits and Fits for Cylindrical Parts.
Last reviewed: October 2026. Every clearance on this page was recomputed from the limits and agrees with the value printed in the Handbook.