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=3/8 inch OD=9.5 mm L=25 mm ID=1/4 inch ID=6.35 mm Diameter Imperial: 3/8 Diameter Metric: 9.5 Overall Length Metric: 25