A serrated connection joins a shaft and a hub (the bored part that sits on the shaft, such as a gear, coupling or flange) with many pointed teeth, so the two parts interlock positively and transmit torque. In engineering, “serrations” usually means this: the connection standardised in DIN 5481 as Kerbverzahnung. It is often mixed up with the involute spline and the straight-sided spline, although tooth form, standard and manufacture differ. This page sorts out the three, names the standards, explains how shaft and hub are made and on which machine types, and covers fits and typical failures. It ends with a short note for owners of such machines. For the wider picture see how gears are made.
What are serrations?
A serrated connection is a special kind of splined connection. It joins shaft and hub by form fit, meaning the interlocking teeth carry the torque. The two flat flanks of a tooth are not parallel, and the teeth are pointed. Under DIN 5481 the shaft teeth have a constant space angle (the angle of the gap between two teeth) of 60°, while the space angle of the hub teeth depends on the number of teeth.
Because many teeth carry at once, medium to large torques can be transmitted, and shaft and hub are weakened less than with a keyed connection. The price: unlike a straight-sided spline, the connection is not designed for axial sliding because of wear. If you need a sliding connection, use a straight-sided spline or an involute spline with a clearance fit.
Serrations, involute splines and straight-sided splines compared
In everyday use, many things are called “serrations” that are really an involute spline or a straight-sided spline. A common mistake in practice is therefore confusing DIN 5480 and DIN 5481.
| Feature | Serrations | Involute spline | Straight-sided spline |
|---|---|---|---|
| Standard | DIN 5481 | DIN 5480 | DIN ISO 14 (replaces DIN 5461 to 5463), DIN 5464 for the heavy series |
| Flank form | flat, non-parallel flanks, pointed teeth | involute flanks, pressure angle 30° | parallel flanks |
| Axially sliding | no (wear) | shiftable with clearance fit | fixed, sliding without load or sliding under load, depending on the fit |
| Shaft teeth | rolling, form milling, hobbing | generating processes, for example hobbing | milling with form or hob cutters, grinding, cold drawing, broaching, rolling |
| Hub teeth | broaching, gear shaping | broaching, gear shaping | broaching, keyway broaching, slotting, EDM |
The involute spline to DIN 5480 uses a uniform pressure angle of 30° and centres on the flanks, in exceptions on the diameter. According to DS Werk, the standard covers module (tooth size in millimetres) 0.5 to 10 and tooth counts from 6 to 82. Part 1 (basics) was last reissued in 2025 and again in 2026, and DIN 5482 has been withdrawn, so always check the current edition for a new design.
Straight-sided splines are mostly made to DIN ISO 14, with inner, flank or outer centring. Inner centring is chosen where accurate runout matters, flank centring for shock-loaded or alternating torque. Involute splines and serrations transmit very large and shock-type torques because of the high tooth count, allow finer adjustment in the direction of rotation, and part diameter and length can be smaller than with a straight-sided spline.
Where serrations and splines are used
They are used wherever a shaft drives a gear, coupling, disc or flange and a key reaches its limit: high and shock-type torques, little space, and where shaft and hub should be weakened as little as possible. Sliding splines are found, for example, on drives that are often assembled and dismantled, such as power take-off drives. A documented failure shows where the limit lies: the drive shaft of a shredder for industrial waste broke in operation exactly at the end of the teeth when foreign material overloaded the machine.
Serrations or a key?
A key is the simplest shaft-hub connection, but it needs a keyway in shaft and hub and passes the torque through a single driver. A serrated connection spreads the load over many teeth and weakens shaft and hub less. In return it is harder to make: hubs are broached or shaped and shafts milled, rolled or ground, while a keyway is cut with a keyway cutter. The toothed connection pays off mainly for high, alternating or shock-type torques and in series; for low load and small quantities, a key remains the more economical solution.
How serrations are made
The shaft: rolling, form milling or hobbing
The shaft teeth are made by rolling, form milling or hobbing. In hobbing, a worm-shaped hob runs against the rotating shaft in a generating motion; with a single-start hob, the workpiece advances by one tooth per revolution. The cut is continuous and stock removal high. In form milling, a disc cutter in the shape of the tooth space cuts each space individually. That works on ordinary milling machines but needs a separate tool for each module and tooth count.
Rolling is a chipless forming process in which the tooth profile is made by plastic deformation. Cold rolling is used for, among others, splines with pointed tooth tips. Rolling machines are a machine family of their own and are not part of our machine-type pages.
If the teeth are to be wear-resistant, they are hardened, often by induction; hardened or especially accurate profiles are then ground. The length a machine can process is a real purchase criterion: it decides which shafts a shop can take on at all.
The hub: broaching or gear shaping
The hub teeth are internal teeth and are mostly broached or gear shaped. In broaching, a tool with several staggered cutting edges removes material one after another and produces the final form; after one pass the profile is essentially finished. It is very fast but needs a profile-specific tool: every change of tooth count or module needs its own broach, so broaching pays off mainly in series. Broaches for DIN 5481 serrated hubs are offered, for example, for profiles from 7 × 8 to 85 × 90.
Gear shaping combines a stroke of the cutter wheel with a rolling motion and a radial infeed. It suits internal teeth in smaller quantities, internal teeth in blind bores and external teeth without run-out. How hub profiles are cut is covered in more detail on how gears are made, which includes a section on internal gears.
Which machine types make serrations?
Which machine a shop needs depends on whether it makes shafts, hubs or both.
| Part | Process | Machine type | Our page |
|---|---|---|---|
| Shaft | Hobbing | Gear hobbing machine | Gear hobbing machines |
| Shaft | Form milling | Milling machine with disc cutter | – |
| Shaft | Rolling | Rolling machine (chipless forming) | – |
| Shaft | Grinding of hardened profiles | Profile or gear grinding machine | Gear grinding machines |
| Hub | Broaching | Broaching machine | Broaching machines |
| Hub | Gear shaping | Gear shaping machine | Gear shaping machines |
In many shops the machines share the work: the shaft goes over the hobbing machine, the hub over the broaching or shaping machine. A shop making only hubs in high quantity gets by with a broaching machine; one needing many different internal profiles in small lots works more flexibly with gear shaping. When valuing such a machine, workpiece diameter, module, tooth length (the travel on shafts, the broaching stroke on hubs), control and the condition of workpiece spindle and rotary table count.
Design and tolerances
The load capacity of a serrated connection is calculated through surface pressure. Calculation programs such as WN8 work out dimensions and load capacity to DIN 5481, based on permissible pressures after Niemann. For involute splines to DIN 5480, the fit is chosen by load:
| Fit | Type | Use |
|---|---|---|
| 9H/9e | clearance fit | shiftable connections |
| 9H/9js | transition fit | range between clearance and interference |
| 9H/9p | press fit | fixed connections not meant to be dismantled |
According to DS Werk, quality grade 9 is sufficient for most industrial applications. Axial and cross bores in the area of the teeth should reach at most 70 to 75 percent of the tooth length, so the load-bearing residual section is not weakened too much.
Typical failures
A typical failure location is not the teeth themselves but the end of the teeth. In the documented shredder case, three faults overlapped at one point: no relief groove, a hardened zone ending exactly at the transition and a deep bore in the toothed area. Each fault alone would have been manageable; together they broke the shaft.
| Fault | Consequence | Remedy |
|---|---|---|
| No relief groove at the end of the teeth | notch factor up to 4; under DIN 743-2, values of 3 to 5 are possible at sharp transitions | relief groove to DIN 509 with a radius suited to the diameter; a larger transition radius where there is room |
| Hardened zone ends at the transition | brittle structure meets a tough core, cracks start under shock load | let the hardened zone run out at least 3 to 5 mm before the end of the teeth |
| Deep end or cross bore | weakened residual section | bore length at most 70 to 75 percent of the tooth length |
| 9H/9e clearance fit on a shock-loaded connection | the fit is meant for shiftable connections, not shock loads | match the fit to load and assembly concept; consider transition or press fit |
| DIN 5480 and DIN 5481 confused | wrong tooth form (involute instead of serrated, or the reverse) | state standard and tooth form clearly on the drawing |
| Serrated connection slid axially | flank wear | use a straight-sided spline or an involute spline with clearance fit |
What this means for used machines
Serrations are made on classic gear machines: a hobbing machine for the shaft, a broaching or shaping machine for the hub. What such a machine is worth on the used market depends not on the profile but on its basic data: workpiece diameter and maximum module, tooth length, control and generation, operating hours and the condition of spindles and guideways. A modern CNC control couples tool and workpiece axes electronically instead of mechanically, which shows in accuracy and tool life. An accuracy record such as an inspection report is among the documents we ask for.
If you own a machine that makes serrations
We buy your gear hobbing machine, broaching machine or gear shaping machine. Sale through our buyer network: commission stated upfront; you are paid before pickup. The offer usually follows 24–48 hours on working days after we have all the details once we have all information, and the whole process usually takes 7 to 15 working days on a direct purchase. On a direct purchase, payment is made by bank transfer before pickup; we organise dismantling and transport, and whether costs are included is stated in the offer upfront.
The overview is on selling gear cutting machines, and what your gear machine is worth lists the value factors.