For use with carbon shafts (1 w/ FW) extension is made of carbon, so there is no discomfort. If the adhesive part is loose, it will stick firmly with the included spacer. The unique hollow/aluminum/carbon composite construction provides firm strength and lightness. Specifications: Material: Aluminum (insert glue) / Carbon (extension part) / Caution: Please stick the aluminum surface of the adhesive part with sandpaper and other materials before gluing. The length can be freely adjusted with a golden saw, etc., but please do not use the adhesive length below the extension length. Insufficient strength may cause damage. Example: NG-Extension 0.5 inch / Adhesive Length 0.25 inch - NG *The outer diameter of the extension part may vary slightly. There may be scratches, burrs, etc. We do not guarantee any injuries or defects during use. We are at your own risk. Thank you for your understanding. The actual color of the product may differ from that of the product due to photography conditions.