Technical Foundation
What Is a Key Stock Assortment?
A key is a straight bar of steel that fits into matched keyways machined into both a shaft and the hub of a gear, pulley or coupling mounted on it, transmitting torque between the two by shear rather than relying on friction alone. Square and rectangular (flat) key stock are both sold as standard-length bars, sized so a given shaft diameter has one standard key cross-section per ANSI B17.1 (inch) or DIN 6885 (metric) sizing tables — an assortment kit typically bundles the common sizes covering a working range of shaft diameters so a maintenance shop doesn't need to individually stock every size.
Material grade matters as much as size: low-carbon steel key stock is standard for general-duty applications, while higher-strength alloy or oil-hardened steel is specified where the key must transmit higher torque without shearing, and stainless steel key stock is chosen for corrosion-prone or washdown environments rather than for strength. Keys are sold slightly oversized and hand-fit or filed to the actual keyway width, since keyway tolerances on shafts and hubs vary — a key that's undersized for the keyway will rock and eventually shear or wear the keyway walls.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Key Profile | Square, rectangular (flat), Woodruff (half-moon) | Woodruff keys suit tapered shafts and self-align; square/rectangular are standard for parallel shafts |
| Size Standard | ANSI B17.1 (inch), DIN 6885 (metric) | Key cross-section is tied to shaft diameter by standard — not arbitrary or interchangeable across standards |
| Material Grade | Low-carbon steel, alloy/oil-hardened steel, stainless steel | Alloy steel resists shear under higher torque; stainless resists corrosion in washdown environments |
| Bar Length | Standard stock lengths (12 in, 1 ft, custom cut) | Cut to the actual hub length needed — stock bars are typically longer than any single application |
| Fit Tolerance | Bar-stock oversize, hand-fit to keyway width | Keyway tolerances vary by manufacturer — fitting prevents a loose key from rocking and shearing |
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Organised by key profile. Pick a sub-category, or tell us the shaft diameter you're keying and let ChatMRO match the correct key size.
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Applications
Where Key Stock Assortments Get Used
Key stock is specified anywhere a shaft needs a positive, non-slip torque connection to a mounted hub, gear, pulley or coupling.
Power Transmission Repair
Replacing sheared or worn keys during pulley, sprocket and coupling reassembly on motors and gearboxes.
Pump & Motor Maintenance
Keying impellers and motor shafts during rebuild and bearing replacement work.
Machine Tool Repair
Keying gears and handwheels onto machine tool spindles and shafts during rebuilds.
Agricultural Equipment Maintenance
Field replacement of sheared keys in PTO shafts and implement drivetrains.
Conveyor & Material Handling Systems
Keying pulleys and sprockets onto head, tail and drive shafts.
General Fabrication & Custom Machinery
Custom-cut key stock for one-off shaft-to-hub connections in fabricated equipment.
FAQ
Key Stock Assortments Questions, Answered
How do I know what size key stock I need for my shaft?
Key size is tied to shaft diameter by standard tables (ANSI B17.1 for inch sizes, DIN 6885 for metric) — measure your shaft diameter, then look up the corresponding standard key cross-section rather than guessing or matching the old key alone if it was already undersized or worn. Most key stock assortments include a size chart referencing shaft diameter directly.
Why did my old key shear, and will a new one just fail the same way?
Keys most commonly shear from being undersized for the actual torque load, being a softer material grade than the application calls for, or from a loose fit that let the key rock under cyclic load rather than sitting solidly in both keyways. If the failure was repeated, consider stepping up to an alloy or oil-hardened key material rather than just replacing with the same low-carbon stock.
What's the difference between a square key and a Woodruff key?
A square or rectangular key is a straight bar fitting a straight keyway cut the full length of the hub, standard for parallel shaft-to-hub connections. A Woodruff key is a half-moon shaped key seated in a matching curved pocket, commonly used on tapered shaft ends because it self-aligns and doesn't rely on the shaft and hub keyways staying in perfect parallel alignment.
Do I need to fit or file key stock before installing it?
Often yes — key stock is sold at a nominal size but keyway width tolerances vary from part to part, so a key that's a hair oversized for a specific keyway needs light filing or stoning to seat properly without excessive force. A key that's too loose in the keyway will rock under load and wear both the key and the keyway walls prematurely.
Should I use stainless steel key stock for a washdown environment?
Yes if corrosion resistance is the priority — stainless steel key stock resists rust in washdown, food processing or humid environments where carbon steel would corrode and eventually seize or swell in the keyway. Stainless is generally not as strong in shear as alloy steel, though, so it's chosen for corrosion resistance rather than for handling higher torque loads.
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