This Trend Collet Sleeve is designed to reduce a 1/2" (12.7mm) collet to accept a 1/4" (6.35mm) cutter. It is recommended for use as a temporary solution, as a collet of the correct size is preferred for optimal performance and durability. The sleeve is not intended for prolonged use or heavy-duty applications. The outer diameter is 12.7mm (1/2"), and the inner bore is 6.35mm (1/4"). The overall length of the sleeve is 30mm.