No# 20 Jacobs super chuck 3/8″-1″ DIA tooling capacity. Has a #3 MT shank. Comes with a #3-#4MT adapter and chuck key. I bought two of these chucks new 35 years ago and used the one your looking at very little. This drill chucks locks down on tooling very well. A rock solid USA made tool. Drill chucks is in very good condition see pictures for details.