Which device is crucial for ensuring that water does not leak around the shaft?

A rubber gasket is critical for preventing leaks around the shaft because it provides a flexible seal that can accommodate any slight imperfections in the surfaces it joins together. When installed, the gasket compresses to fill the gap between the shaft and its housing, effectively creating a barrier against water or other fluids. This is especially important in applications where moisture could cause damage or reduce the efficiency of a machine.

While various sealing devices exist, such as X-ring seals and V-ring seals, which also focus on leak prevention, a rubber gasket is often the go-to choice for general applications due to its ease of installation and ability to form a reliable barrier in a range of conditions. Shaft collars are typically used for positioning and stabilizing a shaft but do not serve the primary function of sealing against fluid leakage. Hence, the rubber gasket stands out as the most suitable option for the specific need of preventing fluid leaks around a shaft.