Guide
What slip fit tolerance should an inch drawing call out, and which ANSI B4.1 RC or LC class matches it?
Slip fit tolerance is the pair of size limits on a shaft and its mating bore that guarantees the shaft slides in by hand with a small, controlled clearance. “Slip fit” is shop talk, not a standard term, so an inch drawing should replace it with a named class from ASME (ANSI) B4.1: usually RC2 or RC3 when the parts move against each other, or LC2 or LC5 when they are located and stay put, written out as limit dimensions on both parts.
By Saola Manufacturing engineering team · Published · Updated
The problem this guide solves is a familiar one. A drawing says “slip fit with mating part” or “sliding fit” and nothing else. One supplier reads that as a line-to-line fit and the shaft seizes on assembly; another reads it as a free running fit and the pin rattles in its bore. Both suppliers can show an inspection report in which every dimension is in tolerance, because the tolerance that mattered was never written down. The fix is cheap: pick a class, publish the limits, and say whether they apply before or after coating.
On this page
What does “slip fit” mean on a drawing, and how do you recognize a fit problem?
“Slip fit” means a clearance fit tight enough to locate the part but loose enough to assemble by hand, and on a drawing it is only enforceable once it is converted into a class and numeric limits. You have a slip-fit problem when parts that each pass inspection still bind, gall, need a mallet, or wobble once assembled.
The ASME B4.1 standard, Preferred Limits and Fits for Cylindrical Parts, covers plain (non-threaded) cylindrical parts up to 20 inches in diameter and sorts clearance fits into two families. Running and sliding fits, RC1 to RC9, are for parts that move relative to each other, such as a shaft turning in a plain bushing or a plunger sliding in a guide. Locational clearance fits, LC1 to LC11, are for parts that are normally stationary but must assemble and come apart freely, such as a locating spigot, a dowel-located cover or a pin in a clevis. Neither family contains a class called “slip fit”.
The symptoms usually show up at incoming inspection or on the assembly line, not in the supplier's report. A shaft that starts into the bore and then locks partway, a slide that is free when cold and tight after a few minutes of running, scoring or pickup on one side of the bore, or a pin that has to be pressed in when the design intended it to drop in all point to too little clearance. Audible rattle, a part that rocks on its locating diameter, or wear marks at both ends of a bushing point to too much. In both cases, the first thing to check is not the parts but the drawing: does it state a class or limits for both diameters, or only the word?
Which ANSI B4.1 RC or LC class matches a slip fit?
For a part that slides or turns, RC2 (sliding fit) is the closest match to what most engineers mean by “slip fit”, with RC3 or RC4 when the parts must run freely. For a part that is located and then stays still, LC2 (hole H7, shaft h6) is a common choice, and LC5 adds a guaranteed minimum clearance.
The standard's own descriptions are the best guide to choosing. Per ASME B4.1, RC1 close sliding fits locate parts that must assemble without perceptible play, and RC2 sliding fits give accurate location with somewhat more clearance: parts move and turn easily but are not intended to run freely, and in the larger sizes they may seize with small temperature changes. RC3 precision running fits are the closest fits expected to run freely, for slow speeds and light journal loads, and RC4 close running fits suit accurate machinery with moderate speeds and loads. RC5 and RC6 medium running fits are for higher running speeds, heavy journal pressures or both; RC7 free running fits are for work where accuracy is not essential or large temperature variations are likely; and RC8 and RC9 loose running fits allow wide commercial tolerances. On the locational side, LC1 to LC4 all have a minimum clearance of zero, so a shaft at its largest limit and a bore at its smallest limit meet line to line. LC5 is the first locational class with a guaranteed gap.
Read the table below in thousandths of an inch. The class sets both the minimum clearance (the allowance) and the maximum clearance, and both grow with diameter, so the same class name does not mean the same gap on a quarter-inch pin and a two-inch shaft. Every value is quoted from the ASME B4.1 tables as reproduced in the standard engineering handbooks.
| Class | Hole / shaft (ABC symbols) | Clearance, 0.40–0.71 in dia. (0.001 in) | Clearance, 0.71–1.19 in dia. (0.001 in) | Clearance, 1.19–1.97 in dia. (0.001 in) | What it is for |
|---|---|---|---|---|---|
| RC1 | H5 / g4 | 0.25–0.75 | 0.3–0.95 | 0.4–1.1 | Close sliding, no perceptible play |
| RC2 | H6 / g5 | 0.25–0.95 | 0.3–1.2 | 0.4–1.4 | Sliding fit: moves and turns easily, not free running |
| RC3 | H7 / f6 | 0.6–1.7 | 0.8–2.1 | 1.0–2.6 | Precision running, slow speed, light load |
| RC4 | H8 / f7 | 0.6–2.3 | 0.8–2.8 | 1.0–3.6 | Close running, moderate speed and load |
| RC5 | H8 / e7 | 1.2–2.9 | 1.6–3.6 | 2.0–4.6 | Medium running, higher speeds or journal pressures |
| RC6 | H9 / e8 | 1.2–3.8 | 1.6–4.8 | 2.0–6.1 | Medium running, as RC5 with wider tolerances |
| RC7 | H9 / d8 | 2.0–4.6 | 2.5–5.7 | 3.0–7.1 | Free running, accuracy not essential or large temperature swings |
| RC8 | H10 / c9 | 3.5–7.9 | 4.5–10.0 | 5.0–11.5 | Loose running, commercial tolerances |
| RC9 | H11 / — | 6.0–12.8 | 7.0–15.5 | 8.0–18.0 | Loose running, widest tolerances |
| LC1 | H6 / h5 | 0–0.7 | 0–0.9 | 0–1.0 | Snug location, can be line to line |
| LC2 | H7 / h6 | 0–1.1 | 0–1.3 | 0–1.6 | Accurate location, hand assembly |
| LC3 | H8 / h7 | 0–1.7 | 0–2.0 | 0–2.6 | Location, wider tolerances |
| LC4 | H10 / h9 | 0–4.4 | 0–5.5 | 0–6.5 | Loose location, economical tolerances |
| LC5 | H7 / g6 | 0.25–1.35 | 0.3–1.6 | 0.4–2.0 | Location with a guaranteed gap |
To turn a class into dimensions, apply each tabled limit to the basic size with its sign, plus or minus, as the notes to the standard's tables instruct. The second table does that, per ASME B4.1, for a 1.000 inch basic size, so you can see what the supplier should be holding on each part.
| Class | Bore limits (in) | Shaft limits (in) | Clearance range (in) |
|---|---|---|---|
| RC2 | 1.0000–1.0005 | 0.9993–0.9997 | 0.0003–0.0012 |
| RC3 | 1.0000–1.0008 | 0.9987–0.9992 | 0.0008–0.0021 |
| RC4 | 1.0000–1.0012 | 0.9984–0.9992 | 0.0008–0.0028 |
| LC2 | 1.0000–1.0008 | 0.9995–1.0000 | 0.0000–0.0013 |
| LC5 | 1.0000–1.0008 | 0.9992–0.9997 | 0.0003–0.0016 |
Why does a slip-fit shaft seize or rattle?
The most common cause is that no class was specified, so the clearance was chosen by whoever machined the parts. After that come coatings that were not allowed for, form errors such as taper or out-of-round, thermal growth between dissimilar materials, and measurement at the wrong temperature or with the wrong method.
1. The fit was never defined. A note such as “slip fit” or “to suit mating part” leaves the machinist to pick both diameters. A shop working to the drawing will often aim for the middle of whatever general tolerance applies, and two general tolerances on a shaft and a bore can easily overlap, which produces interference on some pairs and a loose fit on others.
2. Coating thickness was not allowed for. Anodizing, plating and other finishes add material to the surface, and a diameter grows by twice the build-up on one side. If the drawing does not say whether the limits apply before or after the finish, a fit that measured correctly in the machined state can bind after the finish is applied. The clearance, transition and interference fits guide covers how much each common finish moves a fit.
3. Form error inside the size tolerance. Under ASME Y14.5 the default rule (Rule #1, the envelope principle) says a feature of size at its maximum material limit must have perfect form, which protects a fit. Drawings that invoke ISO GPS standards work the other way: per ISO 8015 the default is the independency principle, so size limits do not control form unless the envelope symbol is added. A bore that is bell-mouthed or a shaft with a slight bow can then pass a two-point size check and still fail to assemble.
4. Thermal growth. Per ASME B4.1, RC2 fits in larger sizes may seize with small temperature changes, and RC3 is not suited to appreciable temperature differences. An aluminum housing on a steel shaft changes clearance as it warms, because aluminum's typical coefficient of expansion is roughly twice that of steel; a fit that is free at room temperature can lock on a cold morning or after a long run.
5. Measurement conditions. Per ASME Y14.5, dimensions and tolerances apply at 20 °C (68 °F) unless the drawing says otherwise, and ISO drawings use the same reference temperature. Parts measured warm off the machine, or measured with a two-point instrument when the fit depends on the full cylindrical envelope, can be reported as good when the assembled pair is not. Burrs at the bore entry or a sharp shaft end do the same thing at the moment of assembly.
Rattle has a shorter list: a class that is looser than the function needs, limits taken from a general tolerance block rather than a fit, or both parts made at their least-material limits.
How do you diagnose a slip fit that seizes or rattles?
Measure both parts at the reference temperature, compute the actual clearance, and compare it with the clearance range of the class the design needs. If the sizes are right but the pair still binds, look at form, coating and burrs before blaming the class.
Work through the checklist in order, because each step rules out a cause cheaply:
- Read the drawing. Is there a class or limit dimensions on both the shaft and the bore, and does a note say whether they apply before or after finishing?
- Let the parts soak to room temperature, then measure the shaft diameter at several positions along its length and around it, and do the same for the bore. Record the largest shaft and the smallest bore, not only the average.
- Subtract to get the actual minimum clearance on the worst pair. Compare it with the table above for the class you intended.
- Check form: taper and out-of-round on both parts, and straightness on long shafts. If the drawing invokes ISO GPS and has no envelope symbol, the supplier was not required to control these within the size tolerance.
- Check coating thickness on both surfaces, and inspect the bore entry and shaft end for burrs or a missing chamfer.
- Try a functional check: a GO plug gauge in the bore and a GO ring gauge on the shaft test the full length at the maximum material limit, which is how a mating part sees them.
A worked example shows how quickly this settles the argument. Suppose the drawing intended RC2 at 1.000 inch, so per ASME B4.1 the shaft limits are 0.9993 to 0.9997 and the bore limits 1.0000 to 1.0005. If the largest shaft in the lot measures 0.9997 and the smallest bore 1.0000, the worst-case clearance, per ASME B4.1 the RC2 minimum, is 0.0003 inch, so the pair should assemble; if it does not, the cause is form, coating or burrs, not size. If the largest shaft measures 1.0001 instead, it is outside the RC2 shaft limit of 0.9997 per ASME B4.1 and the pair has 0.0001 inch of interference: that is a size nonconformance, and it is only a supplier error if the limits were on the drawing.
For parts already made, the usual dispositions are to sort and match pairs by measured size, to rework the part that is cheaper to remove material from (often re-grinding or re-turning the shaft), or to scrap and remake. Whichever you choose, fix the drawing first so the next lot is made to limits rather than to a word.
| Symptom | Most likely cause | What to check | Fix on the drawing or RFQ |
|---|---|---|---|
| Seizes on assembly, sizes all in tolerance | No class; general tolerances overlap | Largest shaft vs. smallest bore | Name an RC or LC class and give limits on both parts |
| Free before finishing, tight after | Coating build-up not allowed for | Coating thickness on both diameters | State limits apply after finish, or mask the fit diameters |
| Starts in, then locks partway | Taper, bow or bell-mouth | Size at several stations; straightness | Keep the envelope requirement, or add cylindricity |
| Free when cold, binds when running | Thermal growth or class too close | Materials and operating temperature | Move from RC2 or RC3 to RC4 to RC7 |
| Rattles or rocks on location | Class too loose, or both parts at least material | Actual clearance vs. intended class | Tighten to LC2 or RC2, or add a positional control |
| Scores or galls on first insertion | Burr or sharp edge at entry | Bore entry and shaft end | Specify a lead-in chamfer and a deburr note |
How do ANSI RC and LC classes map to ISO 286 fits?
Each ANSI B4.1 class is built from the same hole and shaft letters used in ISO 286, so RC4 corresponds to H8/f7, LC2 to H7/h6 and LC5 to H7/g6. The inch values are rounded tables of their own, so convert by class, not by multiplying millimeter limits.
The B4.1 tables label each class with its American-British-Canadian (ABC) hole and shaft symbols, which use the same letter and grade logic as ISO 286-1: H holes start at the basic size, lower-case letters a to g put the shaft below it, and h shafts end at the basic size. Five of the metric preferred fits in ASME B4.2 have a near inch counterpart (the pairing below is by matching letters, not an equivalence stated in either standard), which is useful when a metric drawing and an inch drawing describe the same assembly.
| ANSI B4.1 class | ABC hole / shaft | Nearest metric preferred fit | ASME B4.2 name |
|---|---|---|---|
| RC2 | H6 / g5 | H7/g6 (looser) | Sliding |
| RC4 | H8 / f7 | H8/f7 | Close running |
| RC7 | H9 / d8 | H9/d9 | Free running |
| RC9 | H11 / (no symbol) | H11/c11 | Loose running |
| LC2 | H7 / h6 | H7/h6 | Locational clearance |
| LC5 | H7 / g6 | H7/g6 | Sliding |
Two practical consequences follow. First, when a drawing is in inches, give the inch limits taken from the B4.1 class; writing “H7/g6” on an inch drawing forces the supplier to convert metric deviations and round them, and different people round differently. Second, if the assembly mixes an inch shaft with a metric bore, define the fit on one system only and derive the other part's limits from the stated clearance range.
What should the drawing and RFQ say so the supplier cannot guess the gap?
Put limit dimensions on both the shaft and the bore, state the condition (before or after finish) and the form control, and keep the class name only as a reference. Never leave the word “slip fit” standing alone.
ASME B4.1 is explicit that its class symbols are for reference while designing, not for the detail drawing: Machinery's Handbook, summarizing the standard, notes that only the sizes should be specified on detail drawings. So the requirement on the bore is the diameter as limits, largest over smallest, for example 1.0005 over 1.0000 for an RC2 bore at one inch, and the shaft carries its own limits, 0.9997 over 0.9993. If you want the design intent visible, put the class and the mating part number in a reference note or on the assembly drawing, never in place of the limits. Limit dimensions are better than a nominal size with a plus/minus tolerance here, because the inspector reads the acceptance range directly, and the guide to unilateral, bilateral and limit tolerances explains why.
Add these to the drawing or the RFQ so the fit survives the trip to an overseas shop:
- Both parts. If you only buy the shaft, give the supplier the bore limits of the mating part too, so they can see the intended clearance.
- Coating condition. “Dimensions apply after finish” or “mask this diameter”. If you are not sure which, ask the supplier to propose one in the quote.
- Form. On an ASME drawing, Rule #1 already applies; on an ISO GPS drawing, add the envelope symbol to the fit diameters, or add a cylindricity tolerance that is smaller than the size tolerance.
- Surface and edges. A surface texture requirement on sliding surfaces, a lead-in chamfer and a deburr note on the bore entry.
- Inspection. Mark the fit diameters as key characteristics and say how they will be accepted, for example with plug and ring gauges or measured at several stations.
Tighter classes cost more to make and to inspect, so choose the loosest class that still does the job; the guide to what tight tolerances cost shows where the cost steps are.
Who does what on a Saola order with a slip fit?
The shaft and bore are machined at our lead CNC plant, and any finish on them goes to a partner plant we manage. Before quoting, our engineers flag any fit that is described in words only and ask for the class or limits.
Shafts, pins and bushings are produced by CNC turning, and bores in housings and plates by CNC milling, at T.K Viet Nam Precision Company Limited, our lead CNC plant in Vietnam since 2017. The plant's inspection equipment includes a 2D vision measuring machine, a height gauge and a hardness tester; when a fit needs a dedicated plug, ring or bore gauge, that gauge is agreed at the quote stage rather than assumed.
If a fit diameter is anodized, plated or coated, that step is done by a partner plant that we manage through surface finishing, and the drawing note on the coating condition tells both plants what size to hold. Each quote names the production site and the country of origin for the order. If the drawing still says only “slip fit”, the quote states which class it was priced against so you can confirm it before any metal is cut.
Send the drawing with both mating parts if you have them through the quote form.
Frequently asked
Is a slip fit the same as a sliding fit?
In everyday use, yes, and both are informal. In ASME B4.1 the class named “sliding fit” is RC2, which is the best single translation when the parts move. For a located part that stays still, LC2 is the usual translation.
What is the clearance for a slip fit on a one-inch shaft?
Per ASME B4.1, an RC2 fit at a 1.000 inch basic size gives a clearance of 0.0003 to 0.0012 inch, and an LC2 fit gives 0 to 0.0013 inch. The worked-limits table above lists the bore and shaft limits for both.
Can I write H7/g6 on an inch drawing?
You can, but it invites rounding errors because the deviations are defined in millimeters. On an inch drawing, LC5 is the inch class built from the same H7 and g6 letters, and its limits are published directly in inches.
Does a slip fit tolerance include the coating?
Only if the drawing says so. Without a note, a supplier will usually machine to the limits and then finish, which shrinks the clearance. State whether the limits apply before or after finish, or mask the fit diameters.
When should I use a transition or press fit instead?
Use a transition (LT) or interference (LN, FN) class when the part must not move and does not need to come apart by hand, such as a dowel or a bearing seat. The press fit tolerance guide covers those cases.
Sources
- ASME B4.1, Preferred Limits and Fits for Cylindrical Parts, ASME, 1967 (reaffirmed 2020)
- ASME B4.2, Preferred Metric Limits and Fits, ASME, 1978 (reaffirmed 2020)
- ISO 286-1:2010, GPS — ISO code system for tolerances on linear sizes — Part 1: Basis of tolerances, deviations and fits, ISO, 2010 (confirmed 2026)
- ISO 286-2:2010, Tables of standard tolerance classes and limit deviations for holes and shafts, ISO, 2010 (confirmed 2021)
- ASME Y14.5-2018, Dimensioning and Tolerancing, ASME, 2018 (reaffirmed 2024)
- ISO 8015:2011, GPS — Fundamentals — Concepts, principles and rules, ISO, 2011 (confirmed 2021)