If you're specifying tooling for a shaft-hub connection and aren't sure whether you need a keyway broach or a spline broach, you're not alone. Both cut internal profiles in bores — but they solve fundamentally different engineering problems. Choosing the wrong one means re-tooling, scrap parts, and missed tolerances.
This guide cuts through the confusion. We'll cover what each broach does, when to use which, how their specifications differ, and the applications where each excels.
A keyway broach (also called a keyseater broach or internal keyway broach) cuts a single rectangular slot — the keyway — inside a bore. The broach is pushed or pulled through the bore alongside a bushing that guides it precisely.
The resulting keyway accepts a key (square or rectangular steel bar) that sits half in the shaft keyway and half in the hub keyway. The key transmits torque by mechanical interference — simple, reliable, and easy to assemble.
When engineers specify keyway: The design calls for a removable connection — the shaft and hub need to be disassembled for maintenance, replacement, or adjustment. The key can be removed; a spline cannot.
A spline broach cuts multiple teeth simultaneously around the entire bore circumference — creating an internal spline profile that meshes with an external splined shaft. Unlike keyway cutting (one slot, one broach pass), spline broaching removes material from all teeth in a single pull.
Splines distribute torque across multiple contact points rather than concentrating it at one key. This dramatically increases torque capacity and allows for more precise angular positioning — critical in gearboxes, drive shafts, and precision couplings.
When engineers specify spline: The design requires high torque transmission, precise centering, or the ability to slide axially — as in a gearshift selector or PTO shaft. A single keyway cannot match the load distribution of a spline.
| Factor | Keyway Broach | Spline Broach |
|---|---|---|
| Profile cut | Single rectangular slot | Multiple teeth around bore |
| Torque capacity | Moderate — concentrated at key | High — distributed across all teeth |
| Precision centering | Poor — hub can rock on key | Excellent — self-centering profile |
| Axial sliding | Not designed for sliding | Involute splines allow smooth sliding |
| Assembly / disassembly | Easy — remove the key | Requires full disassembly |
| Cost of tooling | Lower — simpler profile | Higher — complex multi-tooth form |
| Lead time | Shorter — standard sizes in stock | Longer — often custom per module/tooth count |
| Typical applications | Pulleys, gears, sprockets, couplings | Gearboxes, transmissions, EV motors, PTO |
| Standards | DIN 6885, ASA B17.1, JIS B1301 | DIN 5480, ANSI B92.1, ISO 4156 |
| Material options | M2, M35, ASP2030 | M2, M35, ASP2030 |
Keyway connections are the right choice when:
Keyways are ubiquitous in general engineering for good reason. Billions of shaft connections worldwide use them successfully. Don't over-engineer with a spline when a keyway will do the job.
Spline connections are the right choice when:
There's a third option worth mentioning: serration broaches. Serrations are fine-pitch triangular teeth cut around the bore — essentially a very fine spline. They're common in:
Serrations are not designed for sliding — they're pressed or assembled once and hold by form-fit and sometimes interference. If your application is a press-fit hub that must never come loose, serrations provide more grip than a keyway without the cost of a full involute spline.
Whether you're ordering keyway or spline broaches, the steel grade matters as much as the geometry:
When requesting a quote from a broach manufacturer, provide these details:
For keyway broaches: bore diameter, keyway width, keyway depth, tolerance class (JS9/D10/P9), material of the workpiece, and standard (DIN 6885 / ASA B17.1 / JIS).
For spline broaches: bore diameter, module, pressure angle, number of teeth, fit class, spline standard (DIN 5480 / ANSI B92.1 / ISO 4156), and workpiece material / hardness.
The more detail you provide upfront, the faster you'll get an accurate quote — and the less chance of a costly re-make.
SK Broach manufactures both to DIN, ANSI, and JIS standards from our Patiala facility. ISO 9001:2015 certified. Approved vendor to Honda, Maruti, and Mahindra. Same-day quote response.
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