The opening to the hollow core used to be as big as a doorway.

With a raspberry, the torus remains on the plant, leaving a hollow core in the raspberry fruit.

Hollow core doors are much lighter than solid wood doors, cheaper and are easier to install.

Each disc was packaged in a thin plastic slipcase with a hollow core.

Hydraulic-action timers work by energizing the solenoid coil which pulls the hollow core into the center of the coil.