Methods of fixing to a shaft

There are many solutions for attaching a gear to a shaft. Here are a few ideas which should help you in your installation:
Attachment with a fixing screw Attachment with a Key and Circlip
Attachment with a Cotter pin Attachment with a Locking assy.
Attachment with a Locking ring Attachment with a Self-lubricating bush

Assembly with a fixing
screw is very simple. It just
needs a threaded hole to be
machined into the hub, and the
machining of a flattened area
on the shaft. The forces are
concentrated on the edges of
the cup headed screws (GM and SM)


This type of fixing improves adherance
and stops all displacement.
The transmissible torque is limited with
this kind of mounting
It is therefore recommended for the fixing
of low module gear wheels.
The threaded hole is standard on all HPC pulleys.


The use of a key attaches the gear to the shaft by stopping rotation between the two. A groove, or keyway must be machined into the bore and shaft. For manufacturing practicalities, the groove cut into the bore must traverse the whole width of the gear.

A parallel key - is a rectangular
piece of metal, embedded half and
half into the shaft and hub. The machining
of the groove in the shaft is done
with the aid of a two bladed cutting tool.
A keyway of this type is excellent for the transmission of high torque levels.


Disk (or half moon) keys are used for the transmission of weaker couples. The machining of the keyway into the shaft is very easily done using a three bladed cutter.
A keyway does not stop axial movement of the system. Therefore it must be combined with another locking system, such as a thread and bolt, or more simply, by circlips.
  • Attachment with circlips

Circlips, stop axial movement between two componants.
There are two types of circlips, one for shaft mounting and one for inside the bore.


The utilisation of these elements needs a groove to be cut into either the bore or the shaft. They are then fitted axialy, from one end of the shaft or bore with the aid of a specialised tool. Attention, a minimum (or maximum) clearance diameter is needed for the installation.

The use of these componants is often associated with a KEYWAY in the assembly of pulleys or spur gears.
  • Assembly with cotter pins  

The cotter pin has the effect of immobilising one componant with respect to another, of assuring an accurate relative positioning of the two pieces, or of transmitting a movement. It can also play a safety role by shearing away in the event of a violent surcharge.


Essentially, the pin is subject to shearing, and should therefore be used in cases where there is relatively little torque involved. It's usage is not recommended where frequent removal is necessary. The piercing of the pinholes is generally done after assembling the componants in order to assure perfec t alignment.

The use of a cylindrical cotter pin needs the precise machining of a hole through the shaft and gear. A rough hole is good enough because the pins will adjust by deforming in their seating.
This property gives them a very good resistance to vibration.
This type of assembly is excellent for small toothed wheels or pulleys, or gears with low modules.
  • Installation with a Locking assembly.

By tightening the screws, the user deforms a conical ring, and causes a strong force between the shaft and bore. The liasion obtained is complete and rigid (i.e. backlash free) , and easily removed.


By avoiding the manufacturing accidents which can be caused whilst cutting keyways etc?This system actually increases the sectional strength of the shaft and decreases both the concentration of stress points and the phenomenon of metal fatigue cracking.

For equal diameters, the transmissible couple with this method is much higher. Work to be done on the shaft and bore is limited to insuring an H8/h8 tolerance and a surface finish of at least Ra=1,6mm for self-centering assemblies (RT25 and RTL450).

A guide should be envisaged for the other assemblies. These locking assemblies are recommended for all types of toothed wheels, and especially for pulleys, sprockets and gears with large pitches or important modules. 

  • Attachment by locking ring
Attachment by locking ring is a fast and efficient method of attaching all types of toothed wheels. Two solutions exist, locking with half a locking ring (type CT), or locking with the aid of a full collar (CC).

This first solution involves the machining and removal of half of the gear hub and the piercing of two threaded holes in the rest of the hub.


The other solution involves trimming the hub and the machining of two channels - as shown in the diagram

In both cases, the result is a completely rigid joint, which is perfectly suited to the transmission of high levels of torque.

  • Assembly by self lubricating bush.

This very simple system provides a reliable, simple and efficient rotational guidance. It manages to limit friction between the shaft and bore with the aid of two self lubricating bushes (type QAF or QAG), and at the same time, stopping axial movement of the rotating object.

The locking elements the most practical are locking rings (CT or CJ). They have no requirement for special machining and can be positioned at any point on a shaft, allowing for adjustments to the position of the pivot point.

Locking collar CJ :

Locking collar CT  :

The use of self-lubricating Ollite QAG or QFM bushes imposes a maximum tolerance of f7 on the shaft and H8 on the bore (see ISO 2795 and 2796).