What is used to check the gap of breaker points?

The appropriate tool for checking the gap of breaker points is the feeler gauge. This tool consists of a set of thin metal strips of varying thicknesses, which allows for precise measurement of gaps. When adjusting breaker points, it's crucial to achieve the correct gap for optimal performance, and feeler gauges enable the user to insert a specific thickness strip to ensure that the distance between the contact points is set accurately.

Other tools mentioned, like calipers, torque wrenches, and thickness gauges, serve different purposes. Calipers can measure internal and external dimensions, but they are not specifically designed for gap measurements in the context of breaker points. Torque wrenches are used to apply a specific torque to fasteners and do not measure gaps. Thickness gauges measure material thickness for different applications but lack the precise calibration necessary for specific electrical measurements like those needed for breaker points. Thus, the feeler gauge is the ideal choice for this task.