What Are the Drill Bit Lengths on a Screw Machine?

Fractional

• Fractional drill bit length measurements apply to the percentage of an inch represented by the drill bit. These fractional lengths begin at 1/64 of an inch and range up to one full inch. Fractional measurements are common for drill bit lengths because they are easy to communicate, and the larger numbers are easier to remember.

Decimal

• Decimal measurements also come from the inch, but the numbers are much smaller and longer to communicate than fractional measurements. The drill bit decimal measurements begin at .0098 inches and rise to 1.000 inch. Some decimal measurements match up with fractional measurements while others match with wire numbers and letters.

Wire Numbers and Letters

• Some drill bit measurements do not involve or refer to specific lengths. The first wire number is 80 at .0135 inches and decreases to 1 at .2280 inches. It then changes to numbers. At .2340 inches, the wire letter is A and it ranges all the way to Z at .4130 inches.

Metric

• Metric drill bit lengths are not common in the United States. Most other countries around the world use the Metric system instead of the Imperial system. The Metric system is useful if you know how to convert from inches to millimeters. The metric measurements begin at .25 millimeters and range to 25 millimeters.