What tool is used to check a jack hole for plumb?

The correct choice for checking a jack hole for plumb is a tool specifically designed for that purpose — the spider bob. A spider bob utilizes a string and weight system that can easily identify vertical alignment by hanging freely from the top of the jack hole. As the weighted end settles to find the lowest point, it provides a clear reference line that indicates whether the hole is perfectly vertical.

In this context, using a spider bob is especially advantageous for larger job sites or scenarios where precise vertical alignment is critical, as it enables the technician or installer to ascertain plumb without needing to adjust or reposition the tool significantly. Other tools like plumb bobs, measuring tapes, and level gauges have their applications but may not provide the same level of ease and precision in this particular task as the spider bob does.