Description: Electric Drill Chuck Capacity 0.6-6mm Thread 3/8-24UNF 1/4"Hex Shank Power Tools Specification: Main Material: Metal Color Black, Silver Tone Capacity:0.6-6.5mm Mount Thread:3/8-24UNF Interior Hole Diameter 6mm/ 0.24" Exterior Hole Diameter Small: 30mm/ 1.2", Big: 23mm/ 0.9" Total Height 4.7cm/ 1.85" Chuck Key 55 x 35mm/ 2.2" x 1.4" (L*W) Features: For milling machine, lathe, drilling machine, wood working machine. The shank with scrw can be tight and flex for you.