In machining, which term best describes a custom device designed to hold a specific part during operations?

The term that best describes a custom device designed to hold a specific part during operations is "fixture." A fixture is specifically engineered to securely position and support the workpiece in a machine tool, ensuring accuracy and repeatability during machining processes. Fixtures can be tailored to the unique dimensions and shape of the part being machined, providing stability and facilitating efficient operations while preventing movement or vibration.

In contrast, other terms do not accurately represent this concept. A bridge typically refers to a structure that provides support or spans an area but does not imply any specific mechanical function related to holding a part. Support could refer to any method of stabilization, but it lacks the precision and specificity associated with a fixture. Lastly, a bolt denotes a fastener used to secure components together, rather than a device solely used for holding parts during machining. Therefore, "fixture" is the most suitable choice given its role in machining processes.