Reduction sleeve is used to reduce the collet size to take cutters with smaller shanks. Should only be used as a stop-gap, as the the correct size collet is recommended. Should not be used for extensive periods or heavy work. Dimensions: OD=1/2 inch OD=12.7 mm L=30 mm ID=6 mm Diameter Imperial: 1/2 Diameter Metric: 12.7 Overall Length Metric: 30