Superior Electric S4-TL Universal 4 in 1 Drill Chuck Key for Drill Chucks (Large) - Pilot Shank 3.9-6.0-8.0-6.9 D1: 16.3mm (0.642 inch), 17.4mm (0.685 inch), 21.2mm (0.835 inch), 16.2mm (0.638 inch) D3: 3.9mm (0.154 inch), 6mm (0.236 inch), 8mm (0.315 inch), 6.9mm (0.272 inch) Compatible with variety of power and air tool chucks Chuck Key Fits 3/8" & 1/2" Chuck