H22 identifies the nominal hexagonal body-size family of a rock-drill steel; it is normally read across two opposite flat faces, not corner to corner. It does not, by itself, define the machine-side shank length, bit-end taper, overall rod length, flushing-bore diameter or bit size. Buyers should treat each of those as a separate specification field.
This distinction matters because two drill rods can both be described as H22 yet still fail to substitute for one another. One may have a different shank geometry, taper angle, collar detail, flushing passage or working length. The H22 label tells you where to start the identification process—not that the complete tool string is compatible.
What “H22” means
In common rock-tool notation, the letter H denotes a hexagonal drill-steel section and the number identifies its nominal size family. For H22, the practical reference is approximately 22 mm across the flats of the hexagon. “Nominal” is important: it is a designation, not permission to accept any measured value. Finished tolerances, wear limits and inspection locations must come from the controlling drawing, standard, machine manual or approved supplier specification.
The International Organization for Standardization describes ISO 1718:1991 as covering the basic dimensions of drill rods and their tapered connections for percussive drilling. ISO states that the edition was reviewed and confirmed in 2022. A buyer should still identify the exact standard, product drawing and revision required by the purchase order instead of assuming every product marketed as H22 is dimensionally identical.
| Marking element | What it normally describes | What it does not prove |
|---|---|---|
| H22 | Nominal hexagonal drill-steel body family, referenced across flats | Shank length, taper angle, rod length, bore size or bit diameter |
| × 108 mm | Machine-side shank/interface length family used in a complete shank designation | Universal fit in every drill with a nominal H22 chuck |
| 7°, 11° or 12° | Rod-to-bit tapered connection family at the opposite end | Machine-side shank compatibility |
| Rod length | Physical working length according to the supplier's stated measuring convention | Hole depth or usable drilling reach without setup allowances |
| Bit diameter | Nominal cutting diameter of the selected bit | Rod-body or shank dimensions |
| Flush-hole dimension | Internal passage available for air or water | Guaranteed flushing performance without checking the complete path |
Across flats is not across corners
A hexagon has two different convenient outside measurements. Across flats is the shortest distance between two parallel opposite faces. Across corners is the larger distance between opposite vertices. Using the second measurement while comparing it with an across-flats designation can make a correct H22 rod appear oversized.
For a basic receiving check, clean the selected measuring location and place the caliper jaws squarely against two undamaged opposite flats. Keep the jaws away from burrs, heavy scale, forging transitions, the collar and visibly worn chuck-contact areas unless the drawing specifically defines one of those locations. Rotate the rod and repeat the measurement on the other flat pairs to reveal local wear, deformation or measurement error.
- Confirm that the inspection document calls for across-flats measurement.
- Use a calibrated instrument with suitable range and resolution.
- Measure on straight, representative body flats at the drawing-defined location.
- Record the actual values rather than writing only “H22 confirmed.”
- Compare with the controlled tolerance and inspection condition, not a generic internet table.
Do not use this measurement alone to approve a rod. It can identify the body family and detect obvious variation, but it does not verify the full shank, collar, taper or straightness.
Why the body is hexagonal
The flat faces provide positive engagement with a matching chuck or guide system. In a compatible percussive drill, that geometry helps the machine rotate or index the drill steel while the piston delivers repeated blows through the shank. The body must therefore transmit a combination of impact, rotation and feed-related loads while remaining free to move as the drill design requires.
A hex section also gives inspectors clear reference surfaces. Flats can be used to identify the nominal family and observe localized polishing, peening, rounding or twist. However, the external shape does not reveal the material grade, heat-treatment profile, fatigue condition or remaining service life. Those require controlled manufacturing evidence and, where applicable, separate inspection or testing.
What the hollow center does
The center hole is a flushing passage. Air or water moves through the drill steel toward the bit, exits through the bit's flushing ports and helps carry cuttings away from the cutting face. A visible bore in the rod is only one part of that path: the drill's flushing entry, shank arrangement, rod bore, taper end, bit socket and bit outlets must all align and remain open.
H22 does not define the bore diameter. Two rods in the same nominal external family may differ in internal passage, end finishing or flushing arrangement. A replacement should therefore be checked against the machine and bit, especially if the existing setup has weak cuttings return or uses a specific water tube or air-entry arrangement. A full path check should cover the flushing entry, rod bore, taper end, bit socket and bit outlets as one system.
H22, H22 × 108 and an H22 tapered rod are not identical statements
These labels answer different questions:
- H22 describes the nominal hex body-size family.
- H22 × 108 adds a machine-side shank/interface length family.
- H22 tapered drill rod says the rod has an H22 body and a tapered bit connection, but the taper angle still needs to be stated.
- H22 × 108, 11°, 1,600 mm is more informative, but the buyer must still confirm collar geometry, flushing, drawing revision and the measuring convention for length.
This is why a photograph of the rod body or a message saying “send H22” is insufficient for substitution. The machine side and bit side are different interfaces. Review the dedicated H22 × 108 shank compatibility guide when matching a rod to a particular pneumatic rock drill.
Cross-section, shank and taper: three separate zones
| Geometry zone | Main buyer question | Useful evidence |
|---|---|---|
| Hex body | Is the nominal family and across-flats size correct? | Drawing, calibrated across-flats measurements and body-condition photos |
| Machine-side shank and collar | Will the rod enter, retain and receive impact correctly in the specified drill? | Rock-drill model/manual, shank drawing, collar dimensions and reference rod |
| Bit-end taper | Will the selected bit seat on the rod and remain serviceable? | Taper angle, gauge method, controlled male/female drawings and matched sample |
| Internal flushing passage | Does the complete system provide an unobstructed air or water path? | Bore/end inspection, flushing arrangement and compatible bit-port layout |
A correct body size cannot compensate for the wrong collar or taper. Conversely, a bit may appear to start on a taper but still have the wrong angle or contact pattern. Approve each zone independently before treating the assembly as compatible.
How to identify an unknown rod without guessing
1. Record the machine information
Capture the rock-drill manufacturer, exact model, nameplate details and available manual. If the machine identity is uncertain, do not infer the chuck from the rod currently installed; the existing rod may itself be an incorrect substitute.
2. Photograph the complete rod and both ends
Include a full-length view, the striking face, collar, chuck-contact flats, flushing entry, taper and any permanent marking. Add a scale only as a visual reference; photographs are not substitutes for calibrated measurements.
3. Measure the body and shank separately
Measure across flats on the representative body, then capture the drawing-required shank length, collar positions and relevant diameters. Avoid worn or mushroomed surfaces. If no acceptance drawing is available, label the readings as identification data rather than final compliance results.
4. Identify the bit-end taper
Do not determine taper angle from a side photograph. Use the approved gauge, controlled drawing or a verified matched rod-and-bit sample. Keep the male rod taper and female bit socket clean before any fit check.
5. Confirm rod length and flushing arrangement
State how length was measured and identify the flushing entry and exit. Check for blockage, off-center bore, burrs or end deformation that could restrict the path.
Common notation and measurement mistakes
- Measuring across corners: this produces a larger value than across flats and can misclassify the body family.
- Treating 108 mm as rod length: in an H22 × 108 designation, it belongs to the machine-side shank family, not the overall working length.
- Assuming one H22 taper: tapered rods are offered in different angle families; H22 alone does not identify the bit-end connection.
- Using bit diameter to identify the rod: several bit diameters may be offered for one rod family, subject to the approved tool system.
- Measuring a worn chuck zone: service wear can understate the original body size.
- Approving from a single dimension: across-flats size cannot validate collar position, taper contact, straightness or bore continuity.
Specification checklist for an H22 rod inquiry
- Rock-drill manufacturer and exact model
- Required shank designation and controlled drawing or manual reference
- Nominal H22 body family and across-flats tolerance
- Rod type: tapered, integral or another defined construction
- Bit-end taper angle and gauging requirement
- Required rod length and the length-measurement convention
- Bit type and nominal hole diameter
- Air or water flushing arrangement and bore/end requirements
- Quantity, packing, marking and inspection-document requirements
- Photos and measured dimensions from a proven reference rod where available
Frequently asked questions
Does H22 mean the rod is exactly 22 mm everywhere?
No. H22 is a nominal hex-body family commonly referenced across flats. Finished tolerances, transitions and acceptable wear depend on the controlled product drawing or applicable standard. Do not apply the nominal label as an inspection tolerance.
Is an H22 × 108 rod automatically compatible with every H22 rock drill?
No. The designation narrows the machine-side family, but the exact chuck, collar, retaining geometry, flushing entry and approved tool list must still be checked against the specific drill model.
Does H22 identify the taper angle?
No. The hex body and bit-end taper are separate specification fields. State and verify the required taper angle independently.
Why is H22 drill steel hollow?
The central passage carries flushing air or water toward the bit. The H22 designation does not specify the bore size or guarantee that the complete flushing path is compatible and unobstructed.
What should a buyer measure on a sample rod?
Measure the drawing-defined body, shank, collar, taper and length features with suitable calibrated equipment. Check straightness and flushing continuity separately, and record the measurement locations and results rather than only the nominal label.
Match the complete rod, not just the hex label
When requesting a quotation, send the machine model, shank drawing, across-flats requirement, taper angle, rod length, bit diameter and flushing details together. PerfoMax can then evaluate an H22 × 108 mm tapered drill-rod route against the complete interface instead of treating “H22” as a full specification.