To lubricate the ways of a lathe, the gibs of a mill, or the cross slide of a grinder:

Using lubricant from central lubricating systems, often referred to as "one shots," is correct because these lubricants are specifically designed to provide effective and consistent lubrication to critical moving parts in machinery such as lathes, mills, and grinders. Central lubricating systems feed oil or grease in controlled amounts to various machine elements, ensuring proper coverage and reducing wear and friction. This method helps maintain the longevity and efficiency of the machine.

These one-shot lubricants are often formulated to handle the specific requirements of the machinery, including viscosity and the ability to withstand high temperatures and pressures found in machining operations. This makes them preferable in many industrial applications over other types of lubrication methods.

In contrast, the other options may not provide the same level of effectiveness or could potentially lead to negative outcomes. For example, oil from a squirt can may not provide consistent coverage, while multi-purpose grease could be too thick for certain applications or not suitable for the type of movement involved. Water-soluble oil may not offer the necessary protection against wear for the components in question, particularly in environments where heavy loads or high temperatures are present.