Roymech engineering encyclopedia

Metric Taper Keys and Keyway Dimensions


Taper keys provide a mechanical connection between a shaft and hub for transmitting torque. Unlike a parallel key, the taper acts against the hub as the key is driven into position, securing the key and producing a firm shaft-to-hub connection.

Not sure which type of key or spline to use?
See the Key and Spline Selection Guide for an explanation of parallel, taper and Woodruff keys, straight-sided and involute splines, and when each type of shaft-to-hub connection is appropriate.

The dimensional data on this page is based on BS 4235-1:1972 – Specification for metric keys and keyways – Parallel and taper keys. The standard covers square and rectangular taper keys in plain and gib-head forms.

Reference data: Dimensions are in millimetres unless otherwise stated. For manufacture, inspection, procurement or contractual work, verify requirements against the applicable edition of BS 4235-1 and the engineering drawing.

Taper Key and Keyway Geometry

Metric taper keyway dimensions showing shaft and hub geometry

The principal dimensions used in the table are:

  • d – nominal shaft diameter
  • b – key and keyway width
  • h – key height or thickness
  • t1 – shaft keyway depth
  • t2 – hub keyway depth
  • r – keyway corner radius

The shaft diameter determines the standard key section. The table then gives the corresponding keyway width, shaft and hub depths, tolerances and permitted corner radii.

Metric Taper Keyway Dimensions

Shaft Key Keyway
Nominal Diameter
d		 Section
b x h		 Width
Shaft & Hub
b		 Depth Radius
r
Shaft t1 Hub t2
Over Inc Nom Tol (D10) Nom Tol Nom Tol Max Min
6 8 2 x 2 2 +0,06
+0,02		 1,2 +0,1
0		 0,5 +0,1
0		 0,16 0,08
8 10 3 x 3 3 1,8 0,9 0,16 0,08
10 12 4 x 4 4 +0,078
+0,030		 2,5 1,2 0,16 0,08
12 17 5 x 5 5 3,0 1,7 0,25 0,16
17 22 6 x 6 6 3,5 2,2 0,25 0,16
22 30 8 x 7 8 +0,098
+0,040		 4,0 +0,2
0		 2,4 +0,2
0		 0,25 0,16
30 38 10 x 8 10 5,0 2,4 0,40 0,25
38 44 12 x 8 12 +0,12
+0,050		 5,0 +0,2
0		 2,4 +0,2
0		 0,40 0,25
44 50 14 x 9 14 5,5 2,9 0,40 0,25
50 58 16 x 10 16 6,0 3,4 0,40 0,25
58 65 18 x 11 18 7,0 3,4 0,40 0,25
65 75 20 x 12 20 +0,149
+0,065		 7,5 3,9 0,60 0,40
75 85 22 x 14 22 9,0 4,4 0,60 0,40
85 95 25 x 14 25 9,0 4,4 0,60 0,40
95 110 28 x 16 28 10,0 5,4 0,60 0,40
110 130 32 x 18 32 +0,18
+0,080		 11,0 6,4 0,6 0,4
130 150 36 x 20 36 12,0 +0,3
0		 7,1 +0,3
0		 1,0 0,7
150 170 40 x 22 40 13,0 8,1 1,0 0,7
170 200 45 x 25 45 15,0 9,1 1,0 0,7

Taper Key Dimensions

Metric taper key dimensions including gib head

The following table gives the key dimensions, including width and thickness tolerances, chamfer, available length range and gib-head dimensions where applicable.

Width b Thickness h Chamfer s Range Of Lengths L Gib Head h1 Radius r
Nom Tol(h9) Nom Tol(h9) Min Max From Inc
2 0
-0,025		 2 0
-0,025		 0,16 0,25 6 20    
3 3 0,16 0,25 6 36    
4 0
-0,030		 4 0
-0,030		 0,16 0,25 8 45 7 0,25
5 5 0,25 0,40 10 56 8 0,25
6 6 0,25 0,40 14 70 10 0,25
8 0
-0,036		 7 Tol (h11)
0
-0,090		 0,25 0,40 18 90 11 1,5
10 8 0,40 0,60 22 110 12 1,5
12 0
-0,043		 8 0,40 0,60 28 140 12 1,5
14 9 0,40 0,60 36 160 14 1,5
16 10 0,40 0,60 45 180 16 1,5
18 11 0
-0,110		 0,40 0,60 50 200 18 1,5
20 0
-0,052		 12 0,60 0,80 56 220 20 1,5
22 14 0,60 0,80 63 250 22 1,5
25 14 0,60 0,80 70 280 22 1,5
28 16 0,60 0,80 80 320 25 1,5
32 0
-0,062		 18 0,60 0,80 90 360 28 1,5
36 20 0
-0,130		 1,00 1,20 100 400 32 1,5
40 22 1,00 1,20 - - 36 1,5
45 25 1,00 1,20 - - 40 1,5
50 28 1,00 1,20 - - 45 1,5
56 0
-0,074		 32 0
-0,160		 1,60 2,00 - - 50 1,5
63 32 1,60 2,00 - - 50 1,5
70 36 1,60 2,00 - - 56 1,5
80 40 2,50 3,00 - - 63 1,5
90 0
-0,087		 45 2,50 3,00 - - 70 1,5
100 50 2,50 3,00 - - 80 1,5

How Taper Keys Work

A taper key has a tapered surface which engages with the hub. As the key is driven into position, the taper progressively tightens the connection. BSI describes the purpose of the taper as securing the key while firmly engaging the shaft and hub without requiring a set screw.

Taper keys may be supplied as plain taper keys or gib-head taper keys. The projecting head of a gib-head key provides a feature that can assist removal.

The taper geometry is part of the standardized key design and should not be altered simply as a means of adjusting the fit. Correct dimensions, tolerances and assembly practice should be used.

Design Checks

Selection of a standard key size from the shaft diameter establishes the geometry of the connection, but does not by itself establish its load capacity. For a loaded shaft-to-hub connection the designer should also consider:

  • transmitted torque and any shock or reversing loads;
  • key shear stress;
  • bearing or crushing stress at the loaded key faces;
  • key length and available hub length;
  • stress concentration and loss of shaft section caused by the keyway;
  • hub strength around the keyway;
  • assembly, adjustment and removal requirements.

Key and spline strength calculations are provided separately in the Key and Spline Strength page.

Standard Reference

BS 4235-1:1972 – Specification for metric keys and keyways – Parallel and taper keys.

BS 4235-1 covers metric square and rectangular parallel keys and metric square and rectangular taper keys, including plain and gib-head forms.

The standard is currently listed by BSI as Current.

Engineering use: RoyMech provides engineering reference data and guidance. Where dimensions form part of manufacture, inspection, procurement, certification or a contractual requirement, consult the applicable standard and engineering drawing.

Related Key and Spline Information



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