1-1/4 UNC Wet Extension Bar (Diamond Cores) – 500mm. Extension shafts are ideal for adding extra length to your core drill for deep or difficult to reach areas. 500mm extension length (not including thread). Hollow internal to allow for a internal water feed. Can be joined together with others to increase the length. HSW Diamond Tools ensure that everything that we sell meet our highest quality expectations, we extensively test each product on a range of materials from slate, granite to quartz. Unlike other stone tool suppliers we use the tools every day while engraving Highland Slate, we can offer advice and recommendations on all our products based on experience and use.