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Shaft Locking Devices

SIT-LOCK® Keyless Locking Elements

Combining the SIT-LOCK® design of smooth cone action with superior holding power, the hub can be clamped at any position along a shaft, eliminating the need for lock washers, spacers, stop rings, etc.
ATEX compliant 'JXL' torsionally resilient couplings, of pin and bush design
» Easy assembly and disassembly
Both actions take place by locking and unlocking the clamping screws with common tools. The use of a torque wrench is only necessary when a more precise torque is required.

» Superior holding power
The action of the clamping cones creates shaft clamping torque superior to a normal keyed hub.

» Overload protection
When the preset torque is exceeded SIT-LOCK® will slip, preventing the connected elements from being broken.
Note: SIT-LOCK® units are not friction couplings so, excessive slip will cause damage.

» Easy adjustment
Combining the SIT-LOCK design of smooth cone action with superior holding power, the hub can be clamped at any position along a shaft, eliminating the®need for lock washers, spacers, stop rings, etc.
» Precision location
With the SIT-LOCK® smooth cone action, the SIT-LOCK® is ideal for clamping cams, timing devices, and indexing mechanisms accurately and precisely. Temperature-20°C to 150°C.

» Unlimited use possibilities
SIT-LOCK® units are suitable to connect any type of hub (flywheels, chain-wheels, gears, levers, pulleys, eccentrics, coupling, etc).

» Various solutions in stock
Available in stock in 10 different types, SIT-LOCK® units can be utilized in a varied range of industrial applications.
A shaft to hub lock is critical in the design of a mechanical transmission as an unsuitable choice could cause serious damage to the machine or system and result in economic loss.

Shaft-hub coupling designs must take several parameters into account:

» Assessing application loads: torque, bending moment, axial force, radial force. Stresses that may occur simultaneously.
» Alternating loads, sudden starts and stops, very rapid acceleration.
» Fatigue limits of the coupling components.
» Suitable material use.
» Frequent installation and removal requirements.
» Fretting corrosion.
Traditional shaft-hub locking systems include:

» Feather keys
» Key
» Spline coupling
» Interference coupling: forced

Feather Keys

Feather key couplings are the most commonly used.
Assessing the disadvantages:

» High concentration of stress on the shaft and hub due to the high pressure generated on the keyway sides.
» Micro-movements caused by the lack of even contact can cause fretting corrosion making it difficult to remove.
» Not recommended for alternating loads. Over time, the pressure generated on the keyway sides can widen it and cause the shaft or hub to break. Not recommended in damp environments.
» The lack of contact over the shaft-hub surface may lead to oxidation, making it difficult to remove.
» Cannot accept axial loads.
» Not recommended for transmissions that require zero backlash.
» Significant decrease in shaft strength due to the keyway.
» Difficult axial and angular positioning.


Keyed shaft-hub couplings have the same disadvantages as feather key couplings and also cause significant hub-to-shaft concentricity error.

Splined Profile

This coupling has the following disadvantages:

» Fretting corrosion from the lack of contact making it difficult to remove.
» Significant decrease in shaft strength.
» Increased cost as it is difficult to make.
» Play between shaft and hub.
» Difficult angular and axial positioning.
» Not recommended in damp or dusty environments.
» Lack of contact may impair removal.

Interference Fit

Interference fit shaft-hub connections can be achieved by cooling the shaft or heating the hub.
This type of connection is not widely used for the following reasons:

» Requires tight tolerances.
» Difficult to remove.
» Locking area temperature changes.
» The effect of the centrifugal force created by the hub can decrease transmissible torque.
» Increased stress concentrated on the edges.

Shaft strength depends on the type of coupling used As an example, we look at the following data. For a shaft with a diameter d equal to 50 mm, its shaft strength would match the diameter of:

» 39 mm feather key coupling.
» 35 mm splined shaft coupling.
» 46 mm interference fit.
» 49 mm SIT-LOCK® coupling.

SIT-LOCK® Locking Device Coupling

Simply by tightening the screws, SIT-LOCK® keyless locking devices create an axial force on the shaft and the hub that is spread over the entire contact surface. Unlike traditional systems. They offer numerous advantages.

Link to full technical specification catalogue for the SIT-LOCK® Locking Device Coupling

SIT-LOCK® Keyless Locking Elements Application Examples

Locking a crusher flywheel using SIT-LOCK® 4.
SIT-LOCK® 5A used for a timing belt pulley.
Nickel-plated SIT-LOCK® 10 locking two shafts.
SIT-LOCK® 1 used for a conveyor belt pulley.
Locking the drive pulley of a cable car using SIT-LOCK® 4.
SIT-LOCK® 1422 used to lock a hollow shaft.
Mounting two pulleys using SIT-LOCK® 3 without spacers.
SIT-LOCK® 3 used for a disc coupling.
SIT-LOCK® 11 locking the hollow shaft of a planetary gearset.
Locking a bellows coupling using SIT-LOCK® 16.
The 'JXL' range of resilient couplings is able to accept angular, radial and axial misalignment, they are torsionally resilient, non-lubricating and capable of operating between temperatures of –50°C and +105°C.

The elements are flame resistant, anti-static and have NCB acceptance for use underground in coal mines number A2032.

All ATEX compliant 'JXL' anti-static / flameproof couplings are capable of accepting a momentary overload of twice nominal torque.

Couplings are selected on their ability to transmit torque between rotating shafts, with restricting factors being maximum speed and shaft diameter. (See selection notes below).

Supplied in either shaft to shaft version or flange to shaft for drives that require a flywheel connection. Flanges or hubs can be supplied in carbon steel, stainless steel and other exotic materials.

Torque in Nm = Power (Kw) x 9550
Speed (RPM)


18.5 kW at 1500 rpm

18.5 x 9550 = 117.783 Nm

Calculate the torque to be transmitted, determine the required service factor with reference to the duty factor chart, multiply the relevant duty factors together to give the required service factor, multiply the calculated torque by this factor to give the required coupling rating. Select the coupling size with reference to the continuous value, taking into account the bore diameters required.

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