BT Hydraulic Chuck, Standard

https://www.bright-tools.com/products/bt-hydraulic-chuck-standard/

BT hydraulic chucks are effective for reaming, drilling, threading and light milling with end mills at high spindle speeds. They use oil pressure to compress an internal membrane within the holder body, uniformly applying high pressure to grip 360° around the tool shank. This holds cutting tools with a low and repeatable runout of a maximum 3 µm at 3xD (maximum 6µm at 3xD for cylindrical shanks).