https://www.bright-tools.com/products/shrink-fit-er-collet/ Shrink fit collets adapter is used for collet chuck, driven tool holders, and direct clamping in the machine spindle. The tool is clamped precisely in the center of the clamping bore, meaning that it runs true, and when shrunk in, it forms a stable unit with the Shrink fit collet. The short and rigid clamping enables high precision at higher cutting speeds and reduces the wear on the cutting tool dramatically.