Splined Shafts and Bushes

What are splined shafts and bushes?

Splined shafts and splined bushes are matching components used to transmit torque between a shaft and a hub using a series of ridges, called splines, instead of a single key. A splined shaft has evenly spaced splines running along its length, while a splined bush has matching grooves cut into its bore. When the two are fitted together, the splines interlock, so the shaft and bush turn together and can transmit high torque. Depending on the fit, the bush can also slide along the shaft while still transmitting drive.

Because the torque is shared across several splines rather than one key, splined connections are strong, accurate, and well suited to heavy loads, shock loads, and applications where parts need to slide or be removed and refitted often.

Splined bushes are often supplied with a plain round outside, so they can be machined, welded, or pressed into gears, pulleys, sprockets, levers, and custom hubs, giving any component a strong splined bore.

Splined shafts and bushes are usually described by:

• Number of splines - such as 6 splines
• Outside (major) diameter - the diameter across the top of the splines, such as 14 mm or 16 mm
• Inside (minor) diameter - the diameter across the bottom of the splines, such as 11 mm or 13 mm
• Spline width - the width of each spline, such as 3 mm or 3.5 mm
• Overall dimensions - for bushes, the outside diameter and length of the bush body
• Standard - such as ISO 14 or DIN 5463 for straight-sided splines

For example, a 14 × 11 × 3 metric splined bush with 6 splines suits a 6-spline shaft with a 14 mm major diameter, an 11 mm minor diameter, and 3 mm wide splines.

Key features:

• High torque transmission - torque is shared across several splines for a strong connection
• Keyless connection - no separate key or keyway is needed
• Sliding capability - with the right fit, the bush can slide along the shaft while transmitting drive
• Accurate alignment - splines centre the hub on the shaft for smooth, concentric running
• Easy assembly and removal - parts can be fitted and removed without heating or pressing
• Machinable bushes - plain outside diameters allow bushes to be welded or machined into custom parts
• Standard profiles - made to recognised standards for interchangeability

In simple terms, splined shafts and bushes are interlocking parts that let a shaft drive a hub strongly and accurately, with the option of sliding movement.

Why are splined shafts and bushes essential?

Splined shafts and bushes are essential because many drives need to transmit high torque reliably, while allowing parts to slide or be removed easily. A single key can be overloaded, wear its keyway, or shear under shock loads. Splines spread the load across several teeth, giving a stronger, longer-lasting connection that keeps parts accurately centred and handles reversing and shock loads well.

Their main benefits are:

• Greater strength - shares torque across several splines, reducing stress on each one
• Handles shock loads - well suited to heavy-duty, stop-start, and reversing drives
• Sliding drives - allows axial movement for telescopic shafts, gear changes, and clutches
• Accurate centring - keeps gears, pulleys, and hubs running true
• Reduced wear - better load sharing means less wear than a single keyed connection
• Quick fitting and removal - components slide on and off for maintenance
• Custom part making - splined bushes and shaft stock allow custom drives to be built and repaired
• Long service life - strong, durable connections for demanding applications

Splined shafts and bushes are used across a wide range of industries and applications, including:

• Gearboxes - gears, shafts, and sliding gear changes
• PTO drives - power take-off shafts on tractors and agricultural machinery
• Agricultural machinery - drive shafts, implements, and gearbox connections
• Machine tools - spindles, feed drives, and sliding gears
• Hydraulic pumps and motors - drive connections and couplings
• Automotive and transport - drive shafts, clutches, and transmissions
• Construction and plant machinery - drives and power transmission
• Industrial machinery - conveyors, mixers, and custom drives
• Custom fabrication - welding splined bushes into levers, hubs, and adaptors

The main types of splined shafts and bushes

Splined shafts and bushes are usually grouped by their spline profile, form, and material.

By spline profile:

• Straight-sided splines - splines with parallel sides, the most common type for general engineering. Made to standards such as ISO 14 and DIN 5463, commonly with 6, 8, or 10 splines
• Involute splines - splines with curved, gear-like profiles that are self-centring and very strong, used in gearboxes, automotive, and heavy-duty drives. Made to standards such as DIN 5480
• Serrations - fine, triangular splines used for small, compact connections such as levers and adjusters
• PTO splines - standard spline profiles used on tractor power take-off shafts and implements

By form:

• Splined bushes - bushes with a splined bore and a plain round outside diameter, ready to be welded, pressed, or machined into hubs, gears, sprockets, and levers
• Splined hubs - hubs with a splined bore and flanges or bolt holes for mounting
• Splined shafts - shafts with splines along their length, supplied in standard lengths or as bar that can be cut to size
• Splined adaptors - convert one spline profile or size to another

By fit:

• Sliding fit - allows the bush to slide along the shaft while transmitting drive, used in telescopic shafts, sliding gears, and clutches
• Fixed fit - a closer fit for parts that stay in one position on the shaft, giving minimal play

By material:

• Carbon steel - strong and machinable, suitable for welding and general use
• Alloy and hardened steel - for higher strength and wear resistance in heavy-duty drives
• Stainless steel - for corrosion resistance in wet, marine, and food environments

By size system:

• Metric splines - sized in millimetres, such as 14 × 11 × 3 mm or 22 × 18 × 5 mm
• Imperial splines - sized in inches, used on older machinery and some agricultural equipment

How to choose the right splined shafts and bushes?

Choosing the right splined shaft or bush means matching the spline profile exactly and making sure the parts suit the load and application. Work through these points in order:

• Spline profile - identify whether the shaft has straight-sided, involute, serrated, or PTO splines
• Number of splines - count the splines on the shaft
• Major diameter - measure the diameter across the tops of the splines
• Minor diameter - measure the diameter across the bottoms of the splines
• Spline width - measure the width of one spline
• Standard - check the spline standard, such as ISO 14 or DIN 5463, and choose a matching bush or shaft
• Metric or imperial - check whether the splines are metric or imperial
• Fit - choose a sliding fit if the bush needs to move along the shaft, or a fixed fit for parts that stay in place
• Torque and load - choose a size and material strong enough for the torque and shock loads
• Outside diameter and length - for bushes, check the outside diameter and length suit the hub or part you are making
• Welding or machining - choose a steel suitable for welding or machining if the bush will be built into a custom part
• Material - choose carbon steel for general use, hardened or alloy steel for heavy-duty drives, and stainless steel for corrosive environments
• Quality and brand - choose splined parts from reputable suppliers for accurate profiles and consistent fits

FAQ - All you need to know about splined shafts and bushes

What is a splined shaft?

A splined shaft has evenly spaced ridges along its length that fit into matching grooves in a hub or bush. The splines interlock to transmit torque between the shaft and the hub.

What is a splined bush?

A splined bush is a sleeve with a splined bore that fits a matching splined shaft. Many have a plain round outside, so they can be welded, pressed, or machined into gears, pulleys, sprockets, and levers.

What do the sizes on a splined bush mean?

For straight-sided metric splines, sizes are usually given as major diameter × minor diameter × spline width. For example, 14 × 11 × 3 means a 14 mm major diameter, an 11 mm minor diameter, and 3 mm wide splines.

What is the difference between splines and a key?

A key is a single bar that locks a hub to a shaft. Splines spread the load across several ridges, giving greater strength, better centring, and the option of sliding movement.

What is the difference between straight-sided and involute splines?

Straight-sided splines have parallel sides and are common in general engineering. Involute splines have curved, gear-like sides that are self-centring and very strong, making them ideal for heavy-duty and high-speed drives.

How do I measure a splined shaft?

Count the number of splines, then measure the major diameter across the tops of the splines, the minor diameter across the bottoms, and the width of one spline. Compare the measurements with a spline standard chart.

Can a splined bush slide on the shaft?

Yes, if it has a sliding fit. This allows the bush to move along the shaft while still transmitting torque, which is useful for telescopic shafts, sliding gears, and clutches.

Can I weld a splined bush into a part?

Yes, many splined bushes are designed to be welded into hubs, levers, and custom parts. Weld carefully and avoid overheating, which can distort the splines, and check the fit on the shaft afterwards.

Do splined connections need lubrication?

Sliding splines should be lubricated to reduce wear and help them slide smoothly. Fixed splines can benefit from anti-seize or grease to prevent corrosion and make removal easier.

Why are my splines worn?

Common causes include misalignment, lack of lubrication, overloading, shock loads, a loose fit, and contamination. Worn splines can cause play and noise, and should be replaced to prevent damage to other parts.