Final answer:
The measuring instruments used to measure the fit between a rocker arm shaft and its bushing are a micrometer and a bore gauge.
Step-by-step explanation:
When measuring the fit between a rocker arm shaft and its bushing, engineers typically use two measuring instruments: a micrometer and a bore gauge.
A micrometer is used to measure the diameter of the rocker arm shaft, which is the external part that fits into the bushing. The micrometer provides precise measurements to ensure the proper fit.
A bore gauge is used to measure the internal diameter of the bushing. This helps determine if the bushing's size matches the rocker arm shaft.