I put the bearings and mineral spirits or motor spay into a 1/2 oz glass bottle (like this). The ultrasonic waves transfer perfectly through the glass bottle to the cleaning agent to the bearings. I've used weak ultrasonic cleaners before that you could barely tell they are on. This ultrasonic cleaner is so strong it vibrates/tickles to hold onto the glass jar. When they are done and you take the bearings out, you can actually hear how clean they are by the sound they make when you handle them or spin them.