couplings

Please please sit in your library and read & learn couplings, types, application, suppliers etc., before you learn to design one. Moreover, if you design a coupling that will be for your specific application, nothing to do with us.Then again who'd design a coupling when there are millions around to use as per different variation of applications.

Did anyone do their home work tonight?

Torque

rpm

alighnment

http://en.wikipedia.org/wiki/Coupling_%28railway%29

Most important consideraion is "How much flexibility is achievable".

This will decide the alignment requirements and vibration level of two equipments to be coupled.These two factors always will have limitations owing to accuracy which should be taken care by coupling.

Type of equipments to be coupled and the distance between the coupling points are the guiding factors for fixing allowance for coupling flexibility.

Please, study all kinds of couplings available in the market "e.g Fenner" keeping this in mind and pay special attention to recommendations.

Power to be transmitted will decide the size of coupling and other mechanical aspects.

What the heck type of coupling are you talking about? Plumbing, motor to reducer, electrical, railroad cars, etc, etc, etc.

No one can read your mind, you need to ask a specific question describing the application of the coupling you are asking about.