Our plastic half-spheres withstand 180 pounds of force when pumped free of air. Pass them around the classroom, inviting students to try to pull them apart using safety handles, or place in the Vacuum jar and remove the air to equalize the pressure and watch the halves separate. Includes two ABS plastic hemispheres, 4.75" in diameter; brass exhaust valve, 1/4" diameter pressure tubing; wooden handles; illustrated instructions.  Image may vary.