This page provides imperial dimensions for rectangular taper keys, gib-head keys and their keyways to the legacy British Standard BS 46 Part 1:1958. It includes shaft diameter ranges, key sizes, shaft and hub keyway dimensions, tolerances, corner radii and gib-head dimensions.
Reference standard: BS 46 Part 1:1958 – Keys and keyways and taper pins. Specification. Keys and keyways.
The tables below cover rectangular taper keys and the corresponding shaft and hub keyways. Gib-head dimensions are also provided for the key sizes included in the original RoyMech BS 46 reference.
All dimensions in the following tables are in inches.
Use the shaft diameter range to identify the corresponding nominal key width W and height T. The table then gives the dimensional limits for the shaft and hub keyways together with the specified keyway radius.
The numerical values below reproduce the legacy BS 46 dimensional data previously published by RoyMech. Where a component is being manufactured, inspected or replaced against an existing drawing, the original drawing and applicable standard should take precedence.
| Shaft Diameter | Key | Keyway – Shaft | Keyway – Hub | Keyway Radius |
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| D | Width | Height | W | H | W | h | ||||||||
| Over | To / Inc. | W | T | Min | Max | Min | Max | Min | Max | Min | Max | |||
| 1 | 1 1/4 | 5/16 | 1/4 | 0.311 | 0.312 | 0.146 | 0.152 | 0.312 | 0.313 | 0.090 | 0.096 | 0.010 | ||
| 1 1/4 | 1 1/2 | 3/8 | 1/4 | 0.374 | 0.375 | 0.150 | 0.156 | 0.375 | 0.376 | 0.086 | 0.092 | 0.010 | ||
| 1 1/2 | 1 3/4 | 7/16 | 5/16 | 0.437 | 0.438 | 0.186 | 0.192 | 0.438 | 0.439 | 0.112 | 0.118 | 0.020 | ||
| 1 3/4 | 2 | 1/2 | 5/16 | 0.499 | 0.500 | 0.190 | 0.196 | 0.500 | 0.501 | 0.108 | 0.114 | 0.020 | ||
| 2 | 2 1/2 | 5/8 | 7/16 | 0.624 | 0.625 | 0.260 | 0.266 | 0.625 | 0.626 | 0.162 | 0.168 | 0.020 | ||
| 2 1/2 | 3 | 3/4 | 1/2 | 0.749 | 0.750 | 0.299 | 0.305 | 0.750 | 0.751 | 0.185 | 0.191 | 0.020 | ||
| 3 | 3 1/2 | 7/8 | 5/8 | 0.874 | 0.875 | 0.370 | 0.376 | 0.875 | 0.876 | 0.239 | 0.245 | 0.062 | ||
| 3 1/2 | 4 | 1 | 3/4 | 0.999 | 1.000 | 0.441 | 0.447 | 1.000 | 1.001 | 0.293 | 0.299 | 0.062 | ||
| 4 | 5 | 1 1/4 | 7/8 | 1.248 | 1.250 | 0.518 | 0.524 | 1.250 | 1.252 | 0.340 | 0.346 | 0.062 | ||
| 5 | 6 | 1 1/2 | 1 | 1.498 | 1.500 | 0.599 | 0.605 | 1.500 | 1.502 | 0.384 | 0.390 | 0.062 | ||
| 6 | 7 | 1 3/4 | 1 1/4 | 1.748 | 1.750 | 0.740 | 0.746 | 1.750 | 1.752 | 0.493 | 0.499 | 0.125 | ||
| 7 | 8 | 2 | 1 3/8 | 1.998 | 2.000 | 0.818 | 0.824 | 2.000 | 2.002 | 0.539 | 0.545 | 0.125 | ||
| 8 | 9 | 2 1/4 | 1 1/2 | 2.248 | 2.250 | 0.897 | 0.905 | 2.250 | 2.252 | 0.581 | 0.589 | 0.125 | ||
| 9 | 10 | 2 1/2 | 1 5/8 | 2.498 | 2.500 | 0.975 | 0.983 | 2.500 | 2.502 | 0.628 | 0.636 | 0.187 | ||
| 10 | 11 | 2 3/4 | 1 7/8 | 2.748 | 2.750 | 1.114 | 1.122 | 2.750 | 2.752 | 0.738 | 0.746 | 0.187 | ||
| 11 | 12 | 3 | 2 | 2.998 | 3.000 | 1.195 | 1.203 | 3.000 | 3.002 | 0.782 | 0.790 | 0.187 | ||
The following table gives the key dimensional limits, gib-head dimensions and the preferred taper-key and gib-head key lengths contained in the original RoyMech BS 46 reference.
The dimensions A, B, C, D and R refer to the gib-head geometry shown in the diagram. Blank preferred-length entries have been retained where no value was given in the source data.
All dimensions are in inches.
| Key | Gib Head | Preferred Length L |
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| Width | Height | W | T | A | B | C | D | R | ||||||
| W | T | Max | Min | Max | Min | Taper | Gib Head | |||||||
| 5/16 | 1/4 | 0.314 | 0.312 | 0.254 | 0.249 | 3/8 | 7/16 | 1/4 | 0.3 | 1/16 | 3/4 to 3 | |||
| 3/8 | 1/4 | 0.377 | 0.375 | 0.254 | 0.249 | 7/16 | 7/16 | 9/32 | 0.3 | 1/16 | 1 to 4 | 2 to 5 | ||
| 7/16 | 5/16 | 0.440 | 0.438 | 0.316 | 0.311 | 1/2 | 9/16 | 5/16 | 0.4 | 1/16 | 1 1/2 to 4 | 2 1/2 & 3 to 6 | ||
| 1/2 | 5/16 | 0.502 | 0.500 | 0.316 | 0.311 | 9/16 | 5/8 | 3/8 | 0.4 | 1/16 | 1 3/4 to 5 | 2 1/2 & 3 to 6 1/2 | ||
| 5/8 | 7/16 | 0.627 | 0.625 | 0.442 | 0.437 | 11/16 | 3/4 | 7/16 | 0.5 | 1/8 | 1 to 4 | 2 to 6 | ||
| 3/4 | 1/2 | 0.752 | 0.750 | 0.504 | 0.499 | 13/16 | 7/8 | 17/32 | 0.5 | 1/8 | 1 3/4 to 4 | 2 1/2 & 3 to 6 | ||
| 7/8 | 5/8 | 0.877 | 0.875 | 0.630 | 0.624 | 15/16 | 1 | 21/32 | 0.6 | 1/8 | 2 1/2 to 5 | 5 & 6 to 8 | ||
| 1 | 3/4 | 1.003 | 1.000 | 0.755 | 0.749 | 1 1/16 | 1 1/4 | 23/32 | 0.6 | 1/8 | 6 & 7 to 8 | |||
| 1 1/4 | 7/8 | 1.253 | 1.250 | 0.880 | 0.874 | 1 5/16 | 1 1/2 | 27/32 | 0.7 | 1/4 | ||||
| 1 1/2 | 1 | 1.504 | 1.500 | 1.007 | 0.999 | 1 9/16 | 1 5/8 | 1 1/32 | 0.7 | 1/4 | ||||
| 1 3/4 | 1 1/4 | 1.754 | 1.750 | 1.257 | 1.249 | 1 13/16 | 2 | 1 7/32 | 0.8 | 1/4 | ||||
| 2 | 1 3/8 | 2.005 | 2.000 | 1.382 | 1.374 | 2 1/16 | 2 1/4 | 1 13/32 | 0.8 | 1/4 | ||||
| 2 1/4 | 1 1/2 | 2.255 | 2.250 | 1.509 | 1.499 | 2 5/16 | 2 1/2 | 1 9/16 | 0.9 | 3/8 | ||||
| 2 1/2 | 1 5/8 | 2.505 | 2.500 | 1.634 | 1.624 | 2 9/16 | 2 3/4 | 1 11/16 | 0.9 | 3/8 | ||||
| 2 3/4 | 1 7/8 | 2.755 | 2.750 | 1.884 | 1.874 | 2 13/16 | 3 | 1 15/16 | 1.0 | 3/8 | ||||
| 3 | 2 | 3.006 | 3.000 | 2.014 | 1.999 | 3 1/16 | 3 2/8 | 2 1/16 | 1.0 | 3/8 | ||||
These imperial dimensions remain useful when maintaining older machinery, interpreting historic drawings or manufacturing replacement components for equipment originally designed using BS 46.
A taper key develops its fit by being driven axially into the matching shaft-to-hub connection. A gib head provides a feature that assists removal of the driven key. The taper and associated keyway geometry are therefore part of the specified connection and should not be treated as arbitrary adjustments to obtain a desired fit.
When replacing an existing taper key, check the actual shaft and hub keyways, key dimensions and taper against the drawing or original component rather than selecting a replacement from nominal width and height alone.
Do not substitute the nearest metric key solely because its nominal dimensions appear similar. For a new design, current standards and current engineering requirements should normally be considered rather than specifying the withdrawn BS 46 standard simply because the imperial dimensions remain available.