---
title: "H7 Tolerance Explained: What It Really Means for Hole Sizing and Fits"
description: "Sourcing teams often quote H7 holes without checking size range, material, or the mating shaft. H7 defines a tolerance band, not a single dimension—success depends on fit pairing, process capability, and inspection."
url: "https://www.hyneu.com/insights/h7-tolerance-hole-sizing-fits-explained.html"
language: "en"
type: "Article"
category: "Insights"
datePublished: "2026-11-01"
dateModified: "2026-11-01"
brand: "HYNEU"
manufacturer: "HYNEU"
image: "https://static.hyneu.com/uploads/industries/default/JeL3dfkwPBvQn.webp"
---

# H7 Tolerance Explained: What It Really Means for Hole Sizing and Fits

The most common misconception I see in H7 tolerance discussions is the assumption that H7 is a fixed hole size. A buyer sends a drawing note such as "Ø20 H7" and expects every supplier to produce the same measurable hole, with some assumed clearance that will work in every assembly. That assumption breaks down quickly. H7 is not a dimension. It is a tolerance class defined in ISO 286, and its actual width in microns changes with the nominal diameter. Even more important, H7 by itself says nothing about whether the hole runs loose, centers, or presses with a shaft. It only becomes a fit when a shaft tolerance class is paired with it.

This is not a drawing theory problem. It shows up in real sourcing and production as rework, gauge disputes, and parts that pass inspection but fail in assembly. Once you understand what H7 actually specifies, the quoting, machining, molding, and inspection logic becomes much clearer.

![H7 Hole Tolerance in Manufacturing: Machining, Molding, and Inspection](https://static.hyneu.com/uploads/industries/default/JeL3dfkwPBvQn.webp)

## What H7 Specifies in ISO 286

Under ISO 286, a hole tolerance is written as a letter and a number. The letter is the fundamental deviation, and the number is the standard tolerance grade. For H7, the H means the lower deviation is zero. That is the defining feature of the H series: the hole size is never allowed to go below the basic size, also called the nominal size, shown on the drawing.

The number 7 refers to IT7, the standard tolerance grade that sets the total width of the permissible size band. The upper deviation is positive and equals the IT7 value. So a Ø20 H7 hole has a basic size of 20 mm, a lower limit of 20.000 mm, and an upper limit of 20.021 mm, because the IT7 tolerance for the 18 to 30 mm size range is 21 microns. The hole can measure anywhere within that band and still be considered to specification.

This is why H7 is called a hole-basis system. The hole lower limit always equals the basic size, and the fit is then controlled by changing the shaft tolerance. In practical terms, the H hole starts from nominal and only gets larger within the specified tolerance. It never gets smaller than the basic size.

## Why H7 Tolerance Width Changes With Nominal Size

A second common mistake is assuming that H7 means the same micron value for every diameter. A Ø8 H7 hole and a Ø60 H7 hole do not have the same tolerance width. The IT7 tolerance is scaled according to the nominal size range, because manufacturing and measurement difficulty increases as diameter and part size grow.

This has a direct commercial consequence. A buyer who requests H7 on a small bushing bore and H7 on a large housing bore is asking for two very different levels of process control. The numbers below show how the H7 band expands as the basic size increases.

| Nominal Size Range (mm) | H7 Tolerance Band (μm) | Practical Manufacturing Reading |
| --- | --- | --- |
| Over 6 to 10 | 0 to +15 | Tight for most molded plastic holes; normal for reamed metal holes |
| Over 10 to 18 | 0 to +18 | Common for locating pins and small precision bores |
| Over 18 to 30 | 0 to +21 | Typical for shafts, bushings, and spindle seats in machined parts |
| Over 30 to 50 | 0 to +25 | Requires controlled boring or honing; inspection temperature matters |
| Over 50 to 80 | 0 to +30 | Feasible in machining; difficult to hold in molded holes without post-processing |

The table should not be read as a machining guarantee. It is a reference for how quickly the H7 band grows with size. A 25 micron band on a Ø40 hole may sound generous, but it includes roundness, taper, surface finish, and measurement uncertainty. The usable tolerance for the actual mating condition is usually smaller than the total band when the hole is not perfectly cylindrical.

![H7 Tolerance Explained: What It Really Means for Hole Sizing and Fits](https://static.hyneu.com/uploads/industries/default/bTqH9H6JpjJSV.webp)

## H7 Is Only Half of the Fit Decision

A hole tolerance by itself does not create a functional fit. The mating shaft tolerance determines whether the assembly is loose, close, or pressed. When buyers write H7 on a drawing but fail to specify the shaft class, the supplier cannot know what the hole is supposed to do. The same Ø20 H7 hole can be a running fit, a centering fit, or a press seat depending on the shaft.

Common pairings with H7 include the following:

- **H7/g6**: A defined sliding clearance. The shaft is always smaller than the hole, leaving predictable running clearance. Used for spindles, guide pins, and shafts that must rotate or slide freely.
- **H7/h6**: A close clearance fit, sometimes called line-to-line in practice. The shaft upper limit equals the hole basic size, so the fit can range from very small clearance to no clearance at the extreme. Used for centering and precise location without press force.
- **H7/k6**: A transition fit. Depending on actual measured sizes, the assembly may have slight clearance or slight interference. Used where location is critical but light disassembly may be needed.
- **H7/p6**: A light interference or press fit. The shaft is larger than the hole within the tolerance range, requiring force for assembly. Used for bushings, bearing seats, and permanent press locations.

The fit class should come from the design requirement, not from habit. In sourcing, the most frequent problem is a drawing that specifies H7 for the hole and then a shaft tolerance that contradicts the intended function. When in doubt, ask the buyer or design engineer what the assembly must do: rotate, slide, center, or hold permanently.

## Manufacturing Reality: H7 in Machining and Injection Molding

In metal hardware manufacturing, H7 is a familiar and achievable tolerance class for many components, provided the process is chosen correctly. Drilled holes alone usually cannot hold H7 on their own for precision applications. Reaming, boring, and honing are common methods to bring a hole into the H7 band. Tool condition, cutting parameters, machine stability, and coolant temperature all affect the result. A reamed hole can start at the upper limit and shift as the tool warms up, so stable production requires both in-process checking and final inspection.

For injection molded plastic components, the picture is different. A molded hole is produced by a core pin inside the mold. The final hole size depends on the steel core diameter, the plastic shrinkage rate, the material's moisture content, process temperature, and part geometry. Holding an H7 band in a molded hole is generally not realistic as a standard process if no post-machining step is planned. Even when the nominal diameter is tuned to produce an H7-sized hole at the start of a run, process drift and shrinkage variation across batches can shift the hole outside the band.

### What This Means for Buyers of Molded Parts

From a manufacturing and supplier evaluation perspective, an H7 callout on a plastic injection molded hole should trigger a design review. The buyer and supplier need to agree on one of three paths: accept a wider tolerance suited to molding, add a secondary machining operation such as drilling and reaming after molding, or reconsider the material and fit requirement. Treating H7 as a normal molding tolerance leads to rejected batches and production friction.

### Temperature and Material Effects

Another practical point is temperature. Plastic dimensions change more than steel dimensions as ambient or operating temperature changes. A plastic hole that measures within H7 at 25°C may be outside the band at 10°C or 40°C. For metal components, the temperature effect is smaller but still relevant for large housings and tight bands. In both cases, inspection should be linked to a reference temperature, usually 20°C under ISO conditions.

## Inspection and Quality Control for H7 Holes

Measuring an H7 hole is not as simple as taking a caliper reading at one point. A hole can be within diameter tolerance at one cross-section yet fail in roundness or taper at another. Common inspection tools include go/no-go plug gauges for fast production checks and CMM or bore gauges for detailed size and form verification. A go/no-go gauge checks the minimum and maximum material limits but does not reveal taper or ovality.

Quality risks that frequently appear with H7 holes include:

- Burr or raised material at the hole edge, which can distort the first measured value.
- Ovality caused by clamping, thin walls, or uneven cooling in molded parts.
- Taper caused by tool wear in machining or core deflection in molding.
- Measurement at the wrong depth, especially when the hole is deep or interrupted.
- Temperature difference between the part and the measuring instrument.

These risks explain why H7 inspection should be part of the drawing review and not left to final inspection alone. A supplier who understands H7 will ask how the hole is used, how it is measured, and what form errors are acceptable. If those questions do not come up during quotation, the buyer should raise them.

## What Buyers Should Include When Quoting H7 Work

Most H7 sourcing problems begin with incomplete drawing information. A clear RFQ for H7 holes should specify more than the diameter and tolerance class. The following points are the minimum we look for when reviewing H7 requirements from overseas buyers:

- Nominal diameter and the applicable ISO 286 size range, especially if the hole is near a range boundary.
- Mating shaft tolerance class, such as g6, h6, k6, or p6, so the fit is actually defined.
- Functional requirement: sliding, centering, transition, or press assembly.
- Material and, for plastics, the expected operating temperature range.
- Inspection method and reference temperature, especially for tight bands.
- Whether the hole is machined, molded, or molded with secondary machining.
- Quantity and process consistency expectation for batch-to-batch variation.

This level of detail does not make the buyer's job harder. It removes ambiguity and prevents the supplier from quoting a process that cannot hold the requirement. When H7 is used as a general note across an entire drawing without size and fit context, the quotations that come back will either be inflated to cover risk or based on assumptions that may not match the assembly.

## Reading H7 Correctly Changes the Sourcing Decision

From a Zhejiang manufacturing perspective, the biggest difference between a clean H7 project and a difficult one is not the cost of the steel or the injection mold. It is whether the buyer and supplier agree on what the tolerance means before production starts. H7 is a useful, well-established tolerance class. It is not a magic number, and it is not a substitute for a complete fit specification.

For machined metal components, H7 is a normal requirement that can be controlled with reaming, boring, or honing, combined with proper inspection. For injection molded plastic components, H7 should be treated as a special requirement that probably needs post-processing or a tolerance relaxation. In both cases, the buyer should confirm the mating shaft, the function, and the measurement method before the order is released. That single step avoids most H7-related disputes in production.

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