Drill Sizes - Lettered
Drill bits are available in hundreds of sizes, and the size designations include letters, numbers, decimals, and fractions. Decimal drill sizes further include both SAE units and metric units. This particular page presents the lettered drill size series. RF Cafe also has drill size tables for numbered drill size varieties.
These drill bits are almost always of the twist type that advance through the material being bored by turning in a clockwise direction as viewed from the top. They are said to be right-hand drill bits.
| Letter | Diameter (in) | Letter | Diameter (in) | |
| A | 0.234 | N | 0.302 | |
| B | 0.238 | O | 0.316 | |
| C | 0.242 | P | 0.323 | |
| D | 0.246 | Q | 0.332 | |
| E | 0.250 | R | 0.339 | |
| F | 0.257 | S | 0.348 | |
| G | 0.261 | T | 0.358 | |
| H | 0.266 | U | 0.368 | |
| I | 0.272 | V | 0.377 | |
| J | 0.277 | W | 0.386 | |
| K | 0.281 | X | 0.397 | |
| L | 0.290 | Y | 0.404 | |
| M | 0.295 | Z | 0.413 |
Webmaster: Kirt Blattenberger, BSEE, UVM 1989