Much like the Weldon shank side-lock configuration, the PRECI-FLEX® Whistle Notch Adapter is another side-lock chuck that uses a set screw to clamp the drill or endmill. However, unlike the Weldon, the Whistle Notch Adapter has the set screw clamping against the drill or endmill at a 5 degree angle. This 5 degree angle will push the drill or endmill back against a stop in theory. It is up to the end-user to properly set the depth of the stop otherwise the clamping system becomes ineffective. Each adapter is equipped with a set screw at the bottom of the chuck to act as an adjustable stop.