These are CNC Machined Spiral Open-ended grain probes. The openings on the inside tube are machined so that when rotated it opens first at the bottom and then in gradual steps to the top. This assures a fair proportion of grain samples from the bottom levels as well as from the top. The Spiral Probe is highly recommended for sampling grains when foreign material is apt to be heaviest near the bottom of a truck. The construction of the probe is double-tube brass.