To Tap This Size Screw Or Bolt: Use This Drill Bit: Decimal Inches 1/2-13 NC 27/64″ .4219 12mm-1.25mm* 10.9mm .4291 1/2-20 NF 29/64″ .4531 1/2-24 NS 29/64″ .4531 Click to see full answer. Besides, what size hole do I drill for a 1/2 inch bolt?Use the same size drill bit as the diameter of the bolt. If you are using a 1/2″ diameter bolt use a 1/2″ drill bit.Subsequently, question is, how big should a clearance hole be? Tap & Clearance Drill Sizes Screw Size Major Diameter Clearance Drill 0 .0600 .0635 1 .0730 .0760 2 .0860 .0890 3 .0990 .1040 what size bolt fits in a 1/4 hole? For example, a 1/4-inch-diameter bolt with 20 threads per inch is designated as a 1/4-20 bolt.How do you know what size drill bit to use?Hold the shaft of the drill bit up in front of the screw. You should only be able to see the threads of the screw (and maybe a bit of the screw). If you can’t see the threads the drill bit is too big. If you can see too much of the screw, the bit is too small.