Dry and Wet Diamond Core Drill Bit Drilling Tool Accessory Multi Sizes. Our high quality 220×400 mm drill bit is perfect for use with electric core drills for drilling on granite, hard stone, concrete, reinforced concrete, and other hard surfaces. Its durable construction will ensure smooth operation of the drills. We also provide bits of other sizes to meet different drilling needs. As a result packaging may contain advertising/logos from 3rd party companies. You may return the item within 30 days provided it is in its original, unused condition with associated packaging. We are a small family run UK business, aiming to offer the very best customer experience.