Selection Guide

1. Checking required specifications

Confirm your desired specifications that are based on manufacturing machines.

···Check the transfer load, distance and takt time of the workpiece.
···Confirm the machine or unit size (width, height and depth).
···Check the temperature, humidity and environmental conditions.
···Check other conditions (durability, unit service life, etc.).

2.Selecting the transmission method

Decide on an efficient driver such as hydraulics, pneumatics, electric drive, engine, etc. Confirm the structure and the control suited for achieving the required accuracy.

3.Selecting the driver (in case of motor)


Calculate the generated torque by motor torque line and RPM when you set the motor capacity, with or without reduction gear, and its reduction rate.  If there is no manufacturer’s information for the motor, then please use the standard formula below.


Calculate the adjusted torque to coupling Ti referring to the load condition table below.

Characteristics of load K
Stable Under 60% of motor rated torque.
Minimum changes
Gently controlled rotation. 1.5 - 2
Medium changes Acceleration/decelerativ time is long and reverse motion is not frequent. 2 - 3
Large inertia Rapid rotation speed changes with reversing. 3 - 5
Generally standard torque×300% is the maximum torque with servo motor. Recently there are servo motors with 400%−450% drive depending on specifications, therefore design the products with 1.5 times the maximum torque.

Input torque amount of coupling:Ti < Maximum allowable torque capacity

Coupling easy selection table based on servo motor.
Coupling easy selection table based on servo motor.
*Refer to each manufacturer’s catalog for servo motor specification details.

Coupling selection for stepping and encoder motor.

Type Motor shaft diameter Coupling sereies Couplong type
Standard φ4 - 14 AC Series Aluminum disk
Geared φ5 - 18 AC Series Aluminum disk

4.Checking characteristics and specifications

Repetition accuracy

Torsional stiffness and hysteresis affect repetition accuracy of robot hand with servo motor feeding screw. Select the coupling depending on positioning accuracy.

Repetition accuracy:Rigid coupling
Repetition accuracy:Flexible coupling (Single disk)

Repetition accuracy:Flexible coupling (double disk)
Torsional stiffness and hysteresis / Rigid > Single disk > Double disk > Oldham

Moment of inertia

Selecting the small coupling has the advantage of more speed up and decreases the motor power by locating the coupling on the same line, which has an effect on servo motor positioning speed.

Moment of inertia (Steel) / Double disk > Single disk > Rigid


  1. Shaft fit tolerance and surface roughness.
    Shaft fit tolerance and surface roughness.

Installation error

There are two types of couplings; flexible coupling (safety design type with 2-shaft misalignment capacity) and rigid coupling (requires accuracy between 2 shafts with high torque).


Maximum rotation

The coupling maximum rotation figure in the catalog is a stress calculation and not considered movement balance. The coupling is a balanced assembly and can be used without having to balance. However, if the application requires high speed rotation (6000rpm) then balancing will be required after the coupling installation (shaft clamping torque can decrease due to centrifugal force during high speed rotation).

Vibration (oscillation resonance)

Vibration and resonance can result from servo gain adjustment of the servo motor’s feed drive system. If this occurs, check torsional stiffness vibration, moment of inertia and servo-turning function (filter) and reduce servo gain. If vibration occurs with the stepping motor, adjust rotation speed, or recheck vibration resulting from machine torsional stiffness.

5.Selecting coupling series

Select a suitable coupling from the lineup pages (P. 9−P.10) considering the application, installation space, operation, specifications, etc. Features of each coupling can be found at the top of each page. Electroless nickel plating is available for standard disk spring types and stainless and electroless nickel plating for the rigid types.

AS, AD, AL can be ordered by request. Contact us for even a single customized coupling.

6.Checking the load

Stress will be placed on the motor shaft and receiving shaft depending on installation error from assembly accuracy besides using Oldham coupling. Confirm inspection and adjustment of assembly structure design.

Axial extension can result if heat from the motor is transmitted through the motor shaft. This may be avoided by a gap between the axial directions, even with rigid couplings.

7.Final check

Check and confirm the coupling selection and specifications.
Please check step 1 to 6 again for suitability.
If there are no problems, then please check the following points.

Installation depth of shaft

Confirm the shaft insertion amount such that it is within the basic/minimum insertion dimension of each series. (Check with respective product page.)

If insertion is insufficient, the product will be plastically deformed resulting in being unable to be reused. Breakage may result in some cases.

Environmental temperatures

Steel coupling should be used in environments of –40 to +150°C.
Disk spring coupling AC series should be used in environments of –40 to +80°C. (In case temperature rises, transmission torque could be lowered.)
Only E coupling should be used in environments of 0 to +80°C due to plastic parts.


A coupling may be used more than 30 times provided it has been correctly installed and used in normal operation conditions. Screws and surfaces do become scratched so that shaft specs may slowly deteriorate after being reused twice so that replacement of screws are recommended to maintain 100% performance. The E cup may rattle according to the degree of resin wear, therefore, replacement of the body is recommended. Use the looseness prevention treatment bolt five times as a reference.

8.Check the purchasing price

ISEL coupling design is as simple as possible to reduce costs. We maintain high quality and accuracy standards with our original processing to produce high-performance units. Please ask your closest distributor for a quotation.

9.Precautions on use of coupling


Coupling is a friction fastener to couple between shafts. Shaft tolerance, shaft insertion amount, surface roughness and proper tightening of the lock bolt are very important in order to obtain the predetermined performance.

Use of torque wrench / understanding of specified torque

Make sure to use a torque wrench with a torque adjustment scale to tighten the lock bolts to the recommended tightening torque value (confirm according to the specification table of the respective series and the included Instruction Manual). Because the plate type torque wrench specified torque is difficult to check, this may result in trouble such as slip and deformation.

Minimum insertion dimension of shaft / tightening torque, etc.

Refer to the tables on the respective product page, and observe the insertion amount and tightening torque for use. Use with excessive or insufficient inserting amount and tightening torque may result in trouble such as slip, deformation or breakage.

Make sure to confirm that the shaft is inserted within the basic/minimum insertion dimension. If tightened with the shaft improperly inserted, the coupling will be plastically deformed and cannot be inserted into the shaft and hub, resulting in being unable to be reused.

Cleaning of shaft / application of oil

  • Completely wipe away rust, dust and dirt on the surface of the shaft with thinner and lightly apply oil or grease.
  • Slightly apply oil to the bore of the coupling, each taper contact part, screw part of the lock bolt and head seat surface. (Lubricant application location may differ from one product to the next. Make sure to read the Instruction Manual.)
  • It is not necessary to apply oil to aluminum, stainless steel or non-electrolytic nickel plating products.

[WARNING!] Never use molybdenum or an extreme-pressure additive containing oil and grease. Significant reduction in allowable torque and slippage may result.

Other precautions

  • If the shaft has key seats, it can be used in a case where the seat width is nearly equivalent to the JIS standard, however, the allowable torque will be reduced by 15% to 20%. Use it after removing burrs on the key seats.
  • For a hollow shaft (pipe), sufficient surface pressure may not be obtained depending on the wall thickness. Contact us in such a case.
  • Never use unauthorized bolts. Breakage of bolts, and related accidents may result.
  • Confirm that the product is as you ordered, and there is no damage. Use of a product different from an ordered product or damaged product may result in injury to operators or breakage of equipment.
  • When reusing the product, confirm that there is no deformation or missing component to the product.
  • Products of special specifications may differ slightly from what the catalog and Instruction Manual describe. Contact your distributor or our company.


  • Confirm safety before removal and start operation.
  • Turn off the power source (power supply), and confirm that torque and thrust force are not being applied to the coupling and there is no risk of dropping.
  • How to remove and precautions will differ slightly from one product to the next. Make sure to read the Instruction Manual included with the product, and check the details and then remove.