They stacked rocks with center holes (tube or doughnut shaped) from the surface to the deep stone layer as a guide for their drills (similar to today's guide tubes).

Core memory a type of memory that stores information on magnetically charged doughnut shaped cores. mass storage is currently mostly on magnetic disk drum or taoe rather than core.

The Van Allen belts are two doughnut-shaped rings of charged particles-one nestled inside the other-that encircle our planet.