Identified content errors were corrected on 2026-10-25. Sources and scope for this page: NBK parallel-key table (accessed 2026-10-25). The correction record (2026-10-25) reads “Removed unverified inch keyseat depths and metric-equivalence claims. Basic dimensions only; see original drawing and fit tolerances”. Full sources, values and limits on this page.
Page last changed 2026-11-08 · based on Public reference accessed 2026-10-25; scope stated on page
Quick Answer
Selected NBK parallel-key rows — basic dimensions, mm
| Key b × h[1] | Shaft diameter range, as printed[1] | Shaft t1[1] | Hub t2[1] |
|---|---|---|---|
| 3 × 3 # | 8–10 | 1.8 | 1.4 |
| 5 × 5 # | 12–17 | 3.0 | 2.3 |
| 6 × 6 # | 17–22 | 3.5 | 2.8 |
| 8 × 7 # | 22–30 | 4.0 | 3.3 |
| 10 × 8 # | 30–38 | 5.0 | 3.3 |
| 12 × 8 # | 38–44 | 5.0 | 3.3 |
| 14 × 9 # | 44–50 | 5.5 | 3.8 |
Selected parallel-key rows, not the taper-key table. Basic dimensions are not machining limits: use the linked NBK drawing and complete tolerance columns for the required fit. Shaft ranges reproduce the source notation and do not decide boundary ownership. This table does not certify conformity to a particular DIN/JIS edition or convert an inch key into a metric equivalent.
A depth example that cannot be obtained by halving
For the 8 × 7 mm parallel key in this source, shaft t1 is 4.0 mm and hub t2 is 3.3 mm. Half of 7 mm would be 3.5 mm, which matches neither depth. Key height alone therefore cannot define machining dimensions. The source also has separate width fits, radii and tolerances.
Dimensions and strength are separate checks
The joint must transmit the design torque over the effective contact length. In a simplified key model, tangential force F = 2T/d, average shear stress τ = F/(bL), and bearing stress is F divided by the actual engaged bearing area. Check allowable stresses, fatigue, load reversal, shaft/hub strength and fit. Do not use this simplified model to assume a predictable overload-release torque.
Inch keys and other key types
The former inch table mixed unverified standard ranges, half-height depths and claimed metric equivalents; those claims have been removed. For an inch drawing use its specified standard or the mating product drawing. A square key has equal width and height; a rectangular key has unequal dimensions, not necessarily a greater height. Woodruff and taper keys require their own dimensions and load checks.
Sources and limits
NBK: Key and Their Corresponding Keyways, parallel-key table, checked 2026-10-25. University of Florida: Keys and couplings supports separate torque-based shear and bearing analysis.
Frequently Asked Questions
- Can keyway depth be calculated as half the key height?
- Not as a general machining rule. Read shaft and hub depths, their tolerances and the referenced drawing separately.
- Does the key always shear before the shaft?
- No. Failure depends on materials, dimensions, fit and load. Deliberate overload protection requires its own design.
- Is a metric key an interchangeable conversion of an inch key?
- No. Converting units does not establish compatibility of standard widths, depths or fits.
Related
Value Sources
References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.
| # | Source | Type | Revision / method |
|---|---|---|---|
| [1] | NBK parallel-key table | reference | Public reference accessed 2026-10-25 — source |
Data Sources
| Standard | Revision | What it covers on this page |
|---|---|---|
| NBK parallel-key table | Public reference accessed 2026-10-25; scope stated on page | See source scope on page |
Verification scope
- 2026-10-25 — Corrected 2026-10-25. Removed unverified inch keyseat depths and metric-equivalence claims. Basic dimensions only; see original drawing and fit tolerances. Evidence
Corrected 2026-10-25. Removed unverified inch keyseat depths and metric-equivalence claims. Basic dimensions only; see original drawing and fit tolerances.
Cite This Page
Read the source notes, calculation methods and verification scope above before reusing a value. To cite this page:
Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.