Keystock

What is keystock? Keystock is precision square bar used to lock a rotating component to a shaft so the two turn together. A slot called a keyway is machined into the shaft and a matching slot into the hub of the pulley, gear, or sprocket. A length of keystock cut to fit bridges both slots, so torque transfers through the key rather than depending on friction between shaft and hub. It is sized by the square dimension, which must match the keyway. AlbanyCountyFasteners.com stocks zinc plated steel square keystock from 1/8 inch through 1 inch in 1 foot lengths.

Keystock

Zinc Plated Steel

Why a key instead of a set screw?

Because friction is not enough once real torque is involved. A set screw pressing on a shaft holds a light pulley fine, but under load it slips, and once it slips it usually gouges the shaft and the hub creeps out of alignment. A key transmits torque through shear across the key's cross section, which is a far higher capacity path and does not depend on clamping force at all. That is also why keystock is a wear part in a designed sense: the key is intended to be the weakest element, so an overload shears the key rather than twisting the shaft or destroying a gear. Replacing a sheared key is a few minutes of work, replacing a shaft is not.

Why choose keystock

Transmits far more torque than a set screw relying on friction
Positive mechanical drive that will not creep or slip under load
Designed to shear before the shaft or hub does, protecting expensive parts
Cut to length from stock, so one bar covers multiple keyways
Zinc plating gives moderate corrosion protection for indoor machinery

Sizes stocked

Square section in 1/8, 5/32, 3/16, 1/4, 5/16, 3/8, 7/16, 1/2, 9/16, 5/8, 3/4, 7/8, and 1 inch
Supplied in 1 foot lengths, cut to suit your keyway
Match the square dimension to the machined keyway, not to the shaft diameter
Zinc plated steel throughout

Common applications

Locking pulleys, sheaves, and sprockets to drive shafts
Gear and gearbox assembly
Motor and pump shaft connections
Conveyor drives and roller assemblies
Agricultural and industrial machinery repair
Machine building where a positive torque connection is needed

For plain round bar to machine into shafts and pins, see our unthreaded rods. The full bar stock range is on our rods, studs and keystock page.

Related Categories

Keystock FAQs

What size keystock do I need?

Match the machined keyway, not the shaft diameter. Measure the width of the slot in the shaft and order that square size. Standard keyway widths follow shaft diameter conventions, but the only reliable measurement is the slot itself.

Should the key be a tight fit?

Snug on the sides, with a small clearance at the top. The key transmits torque through its side faces, so those need to bear against the keyway walls. A key jammed in top and bottom can hold the hub off its proper seat on the shaft.

How long should I cut the key?

Usually the full length of the hub, so torque distributes along the whole engagement. Shorter keys concentrate load and are more likely to shear. Never let the key protrude past the hub where it could catch.

What is the difference between square and rectangular keystock?

Square keystock is equal in width and height, which is standard on smaller shafts. Rectangular or flat keystock is wider than it is tall and appears on larger shafts where a full square key would cut too deep into the shaft. We stock square.

Why did my key shear?

Usually because it did its job. Keys are often the intended weak point, so a shock load or overload shears the key instead of damaging the shaft or hub. Repeated shearing points to an undersized key or a drive being run beyond its capacity.

Can I use keystock as a plain bar?

It is precision ground square bar, so it works for shims, guides, and general fabrication where a square section is useful. Bear in mind it is sized to keyway tolerances, which is tighter than general purpose bar stock needs to be.