Mechanical Engineering Reference

Standard Keyway Dimensions

Standard parallel key and keyway dimensions used in shaft and hub assemblies. Quick reference table for determining key width (b), key height (h), and nominal keyway depth values based on shaft diameter.

DIN 6885 / ISO 773

Parallel Key & Keyway

Shaft and hub keyway geometry

Dimensions in mm

Application

Shaft / Hub

Key Type

Parallel Key

Primary Width

Units

Keyway Dimensions

Fundamental geometric parameters

Key Width

The nominal width of the key. Directly determines the width of the keyway slot in both shaft and hub.

Key Height

The total nominal height of the standard parallel key.

t₁

Shaft Keyway Depth

The nominal depth of the keyway groove machined into the shaft.

Key Length

Nominal key length, selected based on transmitted torque, hub engagement, and load requirements.

Standard Keyway Dimensions

Shaft diameter → standard key size

Dimensions in mm

Shaft Diameter d	b	h	t₁	t₂	Typical Key Length
6 – 8	2	2	1.2	1.0	6–20
8 – 10	3	3	1.8	1.4	8–25
10 – 12	4	4	2.5	1.8	10–36
12 – 17	5	5	3.0	2.3	12–45
17 – 22	6	6	3.5	2.8	16–56
22 – 30	8	7	4.0	3.3	20–70
30 – 38	10	8	5.0	3.3	25–90
38 – 44	12	8	5.0	3.3	28–110
44 – 50	14	9	5.5	3.8	36–140
50 – 58	16	10	6.0	4.3	45–160
58 – 65	18	11	7.0	4.4	50–180
65 – 75	20	12	7.5	4.9	56–200
75 – 85	22	14	9.0	5.4	63–220
85 – 95	25	14	9.0	5.4	70–250
95 – 110	28	16	10.0	6.4	80–280
110 – 130	32	18	11.0	7.4	90–320
130 – 150	36	20	12.0	8.4	100–360
150 – 170	40	22	13.0	9.4	110–400
170 – 200	45	25	15.0	10.4	125–450

How to Select the Key

1Determine the nominal shaft diameter d.
2Select the standard b × h key profile matching your shaft diameter range.
3Determine the appropriate length L based on torque transmission, allowable surface pressure, and hub width.
4Specify keyway fit tolerances (e.g., P9, N9, or JS9) and reference standards on the engineering drawings.

Engineering Notes

In parallel key joints, torque transmission takes place primarily through compressive contact pressure across the lateral flanks of the key and keyway.

For high-torque duty cycles, key sizing must never rely solely on shaft diameter; both shear stress and bearing pressure must be checked analytically.

Increasing key length beyond standard recommendations does not yield a proportional capacity increase due to non-uniform load distribution. Account for hub geometry, stress concentrations, and shaft notch effects.

Basic Key Strength Checks

Shear Stress

τ = 2T / (d · b · L)

Fundamental simplified equation used to verify approximate shear stress across the key cross-section.

Bearing Pressure

p ≈ 4T / (d · h · L)

Approximate check for compressive contact surface pressure between the key flanks and keyway slots.

Note: These equations are simplified approximations intended for preliminary sizing and initial checks. Detailed machine design must account for precise fit classes, effective contact depth, material yield strengths, alternating loads, and appropriate safety factors.

Standards Reference

This reference table is structured as an engineering summary based on metric parallel key dimensions in DIN 6885 (Form A) and ISO 773. Always verify against the latest revision of the standard and relevant tolerance tables when generating final production drawings.