Final answer:
The correct answer to the question is c. garter spring, which is a type of spring used to hold together parts like carbon packing rings by applying radial pressure.
Step-by-step explanation:
The small spring that surrounds a machine part, such as a carbon packing ring, to hold the part together is known as a garter spring. The garter spring is a coiled steel spring that is connected at the ends to form a circular shape, and its main function is to apply radial pressure to a cylindrical object, ensuring the integrity and sealing ability of the element it is fitted to. This type of spring is commonly used in applications involving shafts or bearing seals, where the consistent pressure provided by the spring is necessary to maintain performance over time.