The TRE8127 Collet Sleeve has the following specifications:
Diameter: 12.7mm (1/2in).
Bore: 8mm.
Overall length: 30mm.

Trend collet reduction sleeve, used to reduce the collet size to take cutters with smaller shanks. Should only be used as a stop-gap, as the correct size collet is recommended.

Should not be used for extensive periods or heavy work.