Which device is used to check the plumb of the jack hole during drilling?

The correct device for checking the plumb of the jack hole during drilling is the spider bob. A spider bob is specifically designed for vertical alignment, and its structure allows it to settle in the jack hole, providing a clear indication of whether the hole is perfectly plumb.

Using a spider bob, an operator can visually see if the drilled hole meets the required vertical specifications, which is crucial for the proper installation of elevator systems, ensuring that the elevator remains level and operates safely.

While a level gauge and plumb bob are tools related to measuring vertical alignment, they serve in slightly different contexts. A plumb bob, typically a weight hung from a string, is often used in a more general sense for aligning verticals and may not be as effective in the specific application of checking the plumb of a jack hole, particularly in the confined environment of the hole itself. A level gauge may be used to assess horizontal surfaces or angles but does not provide the vertical assessment needed in this scenario. The drill extender is used to increase the reach of the drill but does not serve any purpose in checking the plumb of the hole.