A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. In a more general context, a coupling can also be a mechanical device that serves to connect the ends of adjacent parts or objects. Couplings do not normally allow disconnection of shafts during operation, however there are torque-limiting couplings which can slip or disconnect when some torque limit is exceeded. Selection, installation and maintenance of couplings can lead to reduced maintenance time and maintenance cost.

यांत्रिकी के सन्दर्भ में, युग्मक (coupling) वह युक्ति है जो दो शाफ्टों के सिरों को आपस में जोड़ती है ताकि एक शाफ्ट के घुमाने पर दूसरा शाफ्ट भी घूमे। युग्मक ऐसा होना चाहिए कि दोनों शाफ्टों में थोड़ा-बहुत असंरेखीयता (misalignment) हो या दोनों सिरों के बीच थोड़ा-बहुत विस्थापन हो तो भी यह काम कर सके और किसी भाग में अनावश्यक स्ट्रेस न आये।