A coupling is a device used to connect two or more machine shafts for the purpose of transmitting power. Flexible couplings as their name implies can flex slightly which allows them to tolerate a small degree of misalignment. Things to keep in mind when it comes to couplings, they must be sized for proper horsepower, torque speed and environmental conditions. If the shaft diameters and coupling bores are not machined or sized properly machine components could be damaged. Even though flexible couplings can tolerate some misalignment, precisely aligned machines will run longer, smoother, quieter and will require less downtime. Couplings should be inspected and lubricated on a regular basis, just because a coupling can tolerate a certain amount of misalignment other machine components may not. For this reason shaft alignment tolerances are based on the entire machine's health, not just that of a coupling. Couplings are often viewed as simple machine components but installation alignment and maintenance are critical for long-term trouble-free operation. Always refer to manufacturer installation manuals when installing new parts.