Woodruff keys are semi-circular machine keys used to connect a shaft to a hub for torque transmission or location. The circular portion of the key fits into a matching recess machined in the shaft, while the projecting portion engages with the hub keyway.
The dimensional data on this page is based on BS 4235-2:1977 – Specification for metric keys and keyways – Woodruff keys and keyways. The standard specifies Woodruff key dimensions, corresponding shaft and hub keyways, tolerances and the relationship between shaft diameter and key section.
A Woodruff key sits in a circular keyseat in the shaft. Its geometry allows the key to rotate slightly in the shaft seat during assembly, which can assist alignment with the hub keyway. The relatively deep shaft keyseat is an important consideration when assessing the strength and fatigue performance of the shaft.
The principal dimensions used in the tables are:
The table below gives the Woodruff key size together with the corresponding keyway width, fit tolerances, shaft depth, hub depth and corner radius.
| b x h1 x D | Width b | Depth | Radius R | ||||||||
| Nom | Tolerance Class | Shaft t1 | Hub t2 | ||||||||
| Normal | Close | ||||||||||
| Shaft N9 |
Hub Js9 |
Shaft & Hub P6 | Nom | Tol | Nom | Tol | Max | Min | |||
| 1,0 x 1,4 x 4 | 1 | -0,004 -0,029 |
+0,012 -0,012 |
-0,006 -0,0031 |
1,0 | +0,1 0 |
0,6 | +0,1 0 |
0,16 | 0,08 | |
| 1,5 x 2,6 x 7 | 1,5 | 2,0 | 0,8 | 0,16 | 0,08 | ||||||
| 2,0 x 2,6 x 7 | 2,0 | 1,8 | 1,0 | 0,16 | 0,08 | ||||||
| 2,0 x 3,7 x 10 | 2,0 | 2,9 | 1,0 | 0,16 | 0,08 | ||||||
| 2,5 x 3,7 x 10 | 2,5 | 2,7 | 1,2 | 0,16 | 0,08 | ||||||
| 3,0 x 5,0 x 13 | 3,0 | 3,8 | +0,2 0 |
1,4 | 0,16 | 0,08 | |||||
| 3,0 x 6,5 x 16 | 3,0 | 5,3 | 1,4 | 0,16 | 0,08 | ||||||
| 4,0 x 6,5 x 16 | 4,0 | 0 -0,030 |
+0,015 -0,015 |
-0,012 -0,042 |
5,0 | 1,8 | 0,25 | 0,16 | |||
| 4,0 x 7,5 x 19 | 4,0 | 6,0 | 1,8 | 0,25 | 0,16 | ||||||
| 5,0 x 6,5 x 16 | 5,0 | 4,5 | 2,3 | 0,25 | 0,16 | ||||||
| 5,0 x 7,5 x 19 | 5,0 | 5,5 | 2,3 | 0,25 | 0,16 | ||||||
| 5,0 x 9,0 x 22 | 5,0 | 7,0 | +0,3 0 |
2,3 | 0,25 | 0,16 | |||||
| 6,0 x 9,0 x 22 | 6,0 | 6,5 | 2,8 | 0,25 | 0,16 | ||||||
| 6,0 x 11,0 x 28 | 6,0 | 7,5 | 2,8 | +0,2 0 |
0,25 | 0,16 | |||||
| 8,0 x 11,0 x 28 | 8,0 | 0 -0,036 |
+0,018 -0,018 |
+0,015 -0,051 |
8,0 | 3,3 | 0,40 | 0,25 | |||
| 10,0 x 13,0 x 32 | 10,0 | 10,0 | 3,3 | 0,4 | 0,25 | ||||||
Woodruff keys are designated by their width b, height h1 and diameter D. The table below gives the nominal dimensions and tolerances of the standard key sizes, together with the permitted chamfer.
| Width b | Height h1 | Diameter D | Chamfer s | ||||
| Nom | Tol (h9) | Nom | Tol (h11) | Nom | Tol (h12) | Min | Max |
| 1,0 | 0 -0,025 |
1,4 | 0 -0,060 |
4 | 0 -0,120 |
0,16 | 0,25 |
| 1,5 | 2,6 | 7 | 0 -0,150 |
0,16 | 0,25 | ||
| 2,0 | 2,6 | 7 | 0,16 | 0,25 | |||
| 2,0 | 3,7 | 0 -0,075 |
10 | 0,16 | 0,25 | ||
| 2,5 | 3,7 | 10 | 0,16 | 0,25 | |||
| 3,0 | 5,0 | 13 | 0 -0,18 |
0,16 | 0,25 | ||
| 3,0 | 6,5 | 0 -0,090 |
16 | 0,16 | 0,25 | ||
| 4,0 | 0 -0,030 |
6,5 | 16 | 0,25 | 0,40 | ||
| 4,0 | 7,5 | 19 | 0 -0,210 |
0,25 | 0,40 | ||
| 5,0 | 6,5 | 16 | 0 -0,18 |
0,25 | 0,40 | ||
| 5,0 | 7,5 | 19 | 0 -0,210 |
0,25 | 0,40 | ||
| 5,0 | 9 | 22 | 0,25 | 0,40 | |||
| 6,0 | 9 | 22 | 0,25 | 0,40 | |||
| 6,0 | 10 | 25 | 0,25 | 0,40 | |||
| 8,0 | 0 -0,036 |
11 | 0 -0,110 |
28 | 0,40 | 0,60 | |
| 10,0 | 13 | 32 | 0 -0,25 |
0,40 | 0,60 | ||
Select the required Woodruff key size from the applicable shaft diameter and design requirements specified by BS 4235-2. The key designation b x h1 x D identifies its width, height and diameter. The corresponding keyway table then provides the shaft and hub dimensions and tolerances.
Selecting a standard key size establishes the geometry of the connection. It does not by itself demonstrate that the connection has sufficient strength for the applied torque or service conditions.
A Woodruff key has some characteristics that distinguish it from a conventional parallel key. Because it can rotate slightly within its circular shaft seat, it can assist alignment during assembly. Its circular seat can also be useful where a keyway is required close to a shaft shoulder.
The deeper shaft recess is also significant. Removing material from the shaft reduces the remaining section and introduces a stress concentration, so the effect of the keyseat should be considered where shaft strength or fatigue performance is important.
For a torque-transmitting connection the designer should consider:
The suitability of a Woodruff key compared with a parallel key, taper key, spline or another shaft-to-hub connection depends on the complete application. That selection is therefore separate from the dimensional data on this page.
Key and spline strength calculations are provided on the Key and Spline Strength page.
BS 4235-2:1977 – Specification for metric keys and keyways – Woodruff keys and keyways.
BS 4235-2 specifies the dimensional characteristics of Woodruff keys and the corresponding shaft and hub keyways. It also addresses the relationship between shaft diameter and key section for torque-transmitting and positional applications.
BSI currently lists BS 4235-2:1977 as Current, Under Review.
BS 4235-2:1977 was originally identical with ISO 3912:1977 – Woodruff keys and keyways. ISO currently lists ISO 3912:1977 as Withdrawn. The continuing status of the British Standard should therefore be distinguished from the status of the international document.