Technical Foundation
What Is a Woodruff Key Stock?
A Woodruff key is a semi-circular disc of steel that fits into a matching semi-circular keyseat milled into a shaft, with the upper portion projecting to engage a corresponding keyway cut into a hub, gear, pulley or coupling. Its rounded shape lets it self-align and rock slightly within the tapered keyseat, which makes it well suited to tapered shaft ends and light-to-moderate torque applications where a straight key would bind on assembly.
Woodruff keys are specified by a standardized key number under ANSI B17.2 in inch sizes or DIN 6888 in metric sizes, with the number encoding both width and diameter — for example, ANSI key #808 is 1/4" wide by 1" nominal diameter. Because the key number ties directly to a specific keyseat cutter size, ordering the correct number (not just an approximate size) ensures the key fits the keyseat the shaft was actually machined with.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Key Number (ANSI) | e.g. #808 = 1/4" wide x 1" diameter | Number directly specifies width and diameter — must match the keyseat cutter used to machine the shaft |
| Size Standard | ANSI B17.2 (inch) vs. DIN 6888 (metric) | Inch and metric Woodruff keys are not directly interchangeable despite similar appearance |
| Material | Low carbon steel (1018), stainless steel | Stainless is specified for corrosive or washdown environments; carbon steel for general industrial use |
| Keyseat Depth | Standard vs. shallow cut depending on shaft diameter | Keyseat depth relative to shaft diameter affects remaining shaft strength — must follow the standard for that key number |
| Fit Class | Sized for a light interference or sliding fit in the seat | Fit affects how the key seats and how much play exists before the hub keyway engages |
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Applications
Where Woodruff Key Stock Get Used
Woodruff keys are specified wherever a hub needs to be positively located on a tapered or stepped shaft without full straight-key length.
Pump & Motor Shaft Assemblies
Locating impellers, couplings and pulleys on tapered pump and motor shaft ends.
Gearbox & Power Transmission
Securing gears and sprockets to stepped shafts in light-to-moderate torque drivetrains.
Automotive & Small Engine Assembly
Woodruff keys locating flywheels, cam gears and accessory pulleys on crankshafts.
Machine Tool Spindles
Keying pulleys and gears onto machine tool spindles and countershafts.
Agricultural Equipment
Keying pulleys and sprockets on PTO shafts and implement drivetrains.
General MRO & Repair
Stocked key assortments for maintenance crews replacing worn or sheared keys on rotating equipment.
FAQ
Woodruff Key Stock Questions, Answered
How do I identify the Woodruff key number I need?
ANSI Woodruff key numbers encode both dimensions — the last two digits give the nominal diameter in eighths of an inch, and the digits before that give the width in thirty-seconds of an inch. For example, key #808 is 8/32" (1/4") wide by 8/8" (1") diameter. If replacing an existing key, measuring the old key's width and diameter and matching to the nearest standard size is the most reliable method.
Are metric and inch Woodruff keys interchangeable?
No — ANSI B17.2 (inch) and DIN 6888 (metric) Woodruff keys use different dimensional series and are not directly interchangeable even at similar nominal sizes, since the width, diameter, and keyseat depth relationships differ between the two standards. Always match the key standard to the standard the shaft and hub keyseats were machined to.
Why use a Woodruff key instead of a straight key?
A Woodruff key's semi-circular shape allows it to self-align and rock slightly within its seat, making it well suited to tapered shaft ends and assemblies where a straight key would bind during hub installation. It's generally used for lighter-to-moderate torque applications; for high-torque power transmission, straight (parallel) keys are usually preferred since more of the key's length engages the shaft.
What material should I use for a Woodruff key?
Low carbon steel (typically 1018) is standard for general industrial applications. Stainless steel is specified where the assembly is exposed to moisture, washdown, or corrosive environments, such as food processing or outdoor pump equipment, to prevent the key seizing in its seat from corrosion.
Can I cut a Woodruff keyseat with a standard end mill?
No — Woodruff keyseats require a dedicated Woodruff keyseat cutter, a specialized side-and-face cutter matched to the specific key number, which produces the correct semi-circular seat profile and depth. Using a standard end mill will not produce the correct seat geometry for the key to seat properly.
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