A 2.5" outer-diameter high-bounce rubber ball, sold as a small utility accessory alongside Delta Epsilon borehole logging equipment. Some field crews use a ball like this as a low-cost way to check that a borehole or well casing is clear before lowering a sensitive (and expensive) logging probe down it — though this specific practice isn't documented in Delta Epsilon's own manuals, so treat it as a common field habit rather than a required procedure.

Sold individually.