For example, if you need a 4-inch hole, choose a 4-inch or slightly larger drill bit to allow for some margin and ensure a precise fit for the posts. Select the Appropriate Drill Bit Type. The type of drill bit you choose depends on the material you’re drilling through. For wooden fence posts, a standard wood drill bit is suitable., Here’s how you can select the proper drill bit for your fence post drilling needs: Consider the Post Material. Before selecting a drill bit, consider the material of your fence post. For wooden posts, a standard twist drill bit works well. If you have metal posts, opt for a cobalt or titanium drill bit to ensure clean and precise holes., Earth Auger Fence Post Hole Borer Ground 52cc Petrol Spiral Digger 3 Drill Bits Attachments 4 6 8 Inch Extension Pole 80cm 3HP 9000rpm 2 Stroke 1.2L 1.6kw Free Safety Accessories & Tool Kit, Faithfull Earth Auger Drill Bit 80 x 450mm For fence posts boreholes FAIEA80450. Brand new · Faithfull. £17.19. Free postage. Click & Collect, Adaptability-Post hole diggers that adapt with most regular auger bits are more preferable. Certifications-Depending on where you live, certifications like CARB (California) may interest you. Tips on digging on rocky ground. Bits (where applicable)-Cheap bits won’t cut it. A good quality SDS-type bit will do more holes in stone and won’t be , .