Keyway & Key Size Chart — DIN & ANSI

Keyway and key size lookup

Search by shaft diameter, then filter metric or inch rows. The chart returns the key width and height, the shaft keyseat depth, and the hub keyway depth. It also shows the standard family and the boundary rule so you can see why a row applies.

Metric rows are scoped to DIN 6885-1 high-form parallel keys. Inch rows are scoped to ANSI/ASME B17.1. These families are kept separate because their shaft ranges, key proportions, tolerances, and dimensioning conventions are different.

How to select a key from shaft diameter

1. Measure or read the finished shaft diameter at the key location.
2. Identify the unit system and standard family on the drawing.
3. Find the row whose shaft-diameter range contains the value.
4. Use the listed key width and height for the shaft and hub.
5. Use the shaft and hub depth columns independently when modeling or machining the keyways.
6. Confirm width tolerance, side fit, key length, corner treatment, and torque capacity before release.

Read the range boundary carefully

For the selected DIN rows, the first band includes its lower and upper boundary. Later bands use an exclusive lower boundary and an inclusive upper boundary. In practical terms, a shaft exactly 8 mm belongs to the 6 ≤ d ≤ 8 mm row; a shaft exactly 10 mm belongs to the 8 < d ≤ 10 mm row. A value just over 8 mm does not use the first row.

This rule matters when a shaft lies at a standard step. Do not round a measured diameter into a neighboring band. If the shaft is close to a boundary, use the actual measurement, the applicable tolerance, and the licensed standard row.

Shaft keyseat depth versus hub keyway depth

The shaft keyseat is the groove cut into the shaft. The hub keyway is the groove cut into the bore. They do not necessarily have the same depth. A key is shared between the two grooves, so using the shaft depth for the hub or the hub depth for the shaft can change the key’s engagement and the finished radial position.

For the 8 × 7 mm DIN row, the bounded reference gives a 4.0 mm shaft keyseat depth and a 3.3 mm hub keyway depth. For the 1/4 × 1/4 in ANSI row, the selected reference gives 1/8 in for both depths. Those examples do not establish a rule that every key is half in each part.

Metric DIN and inch ANSI families

DIN 6885-1 uses metric shaft bands and rectangular keys such as 8 × 7 mm. ANSI/ASME B17.1 uses inch shaft bands and square or rectangular key sizes such as 1/4 × 1/4 in. Do not convert a metric shaft into inches and then select an ANSI row unless the drawing explicitly calls for that standard.

Keyway width tolerance and side fit also affect assembly. A normal fit, close fit, or interference condition can use different keyway-width classes. The chart keeps the width-class note visible but does not replace the tolerance table in the standard.

CAD and manufacturing interpretation

Model the shaft groove and hub groove as separate features. Apply the shaft keyseat depth from the shaft datum and the hub keyway depth from the bore datum. Check the radial stack with the actual key height, any top clearance, and the specified side fit.

Key length is a separate design choice. Select a standard stock length that fits the hub and meets the calculated shear and bearing requirements. A key size chart does not prove that a joint can transmit the required torque. Check shaft diameter, hub material, key material, load reversals, fretting, and the number of keys.

Common mistakes

• Using the hub keyway depth as the shaft keyseat depth.
• Selecting a key from the nearest metric row when the drawing requires ANSI B17.1.
• Ignoring the exact range boundary and choosing the wrong key step.
• Assuming key height equals either groove depth for every standard.
• Choosing key length from shaft diameter without checking hub length and torque.
• Treating a standard key size as a complete shaft-strength calculation.

For the related fastener and shaft-hardware envelope, use the bolt and wrench size chart. For rotating power-transmission topics, the future sprocket and bushing charts should be kept aligned with the same shaft and key standard rather than mixed into this lookup.

Sources and limits

The metric scope follows DIN 6885-1:2021-11. The inch scope follows ASME B17.1-1967 (S2023). The bounded rows are cross-checked against the J.W. Winco DIN table and the Lowell ANSI reference. Licensed standard tables and the production drawing control final dimensioning.

Frequently asked questions

What key fits a 25 mm shaft?

In the bounded DIN 6885-1 reference, 25 mm is in the 22 < d ≤ 30 mm band, which uses an 8 × 7 mm key, a 4.0 mm shaft keyseat, and a 3.3 mm hub keyway.

Are shaft and hub keyway depths the same?

Not necessarily. Read the two depth columns separately. DIN rows often use different shaft and hub depths; an ANSI square-key example can show equal nominal depths.

What happens at exactly 8 mm?

In this bounded DIN range model, exactly 8 mm belongs to the 6 ≤ d ≤ 8 mm row. The next row starts above 8 mm and ends at 10 mm. Confirm the exact licensed table before machining.