Screw Machine Drill Bit Chart - Stub Drill Lengths
Use this screw machine drill bit chart to find drill diameters, flute lengths, and overall lengths for fractional, numbered (wire gauge), and letter stub drills. Screw machine drills—also called stub length or stubby drill bits—are shorter than standard jobber length drills. Their compact design provides greater rigidity and helps reduce deflection when drilling in tight spaces.
Stub drills are commonly used in machine shops, screw machines, automotive work, and other applications where spindle clearance is limited. They are available in High Speed Steel (HSS) and Cobalt options. Choose the material based on your workpiece and drilling requirements.
Shop Screw Machine (Stub Length) Drill Bits
How to Use the Screw Machine Drill Bit Chart
- Drill size: The nominal diameter, listed as a fractional inch, number (wire gauge), or letter size.
- Decimal equivalent: The drill diameter expressed in decimal inches.
- Flute length: The length of the fluted portion of the drill.
- Overall length: The length of the entire drill bit, from tip to shank end.
Find your drill size in the appropriate section and read across for its flute and overall lengths. All dimensions in the tables below are in inches. Actual dimensions may vary by manufacturer and product series; confirm the product specifications when precise clearance or drilling depth matters.
Fractional Screw Machine Drill Lengths
| Drill Size | Decimal (in) | Flute (in) | Overall (in) | Drill Size | Decimal (in) | Flute (in) | Overall (in) |
|---|---|---|---|---|---|---|---|
| 3/64" | 0.0469 | 1/2" | 1-3/8" | 11/16" | 0.6875 | 2-7/8" | 4-5/8" |
| 1/16" | 0.0625 | 5/8" | 1-5/8" | 45/64" | 0.7031 | 3" | 4-3/4" |
| 5/64" | 0.0781 | 11/16" | 1-11/16" | 23/32" | 0.7188 | 3" | 4-3/4" |
| 3/32" | 0.0938 | 3/4" | 1-3/4" | 47/64" | 0.7344 | 3-1/8" | 5" |
| 7/64" | 0.1094 | 13/16" | 1-13/16" | 3/4" | 0.75 | 3-1/8" | 5" |
| 1/8" | 0.125 | 7/8" | 1-7/8" | 49/64" | 0.7656 | 3-1/4" | 5-1/8" |
| 9/64" | 0.1406 | 15/16" | 1-15/16" | 25/32" | 0.7812 | 3-1/4" | 5-1/8" |
| 5/32" | 0.1562 | 1" | 2-1/16" | 51/64" | 0.7969 | 3-3/8" | 5-1/4" |
| 11/64" | 0.1719 | 1-1/16" | 2-1/8" | 13/16" | 0.8125 | 3-3/8" | 5-1/4" |
| 3/16" | 0.1875 | 1-1/8" | 2-3/16" | 53/64" | 0.8281 | 3-1/2" | 5-3/8" |
| 13/64" | 0.2031 | 1-3/16" | 2-1/4" | 27/32" | 0.8438 | 3-1/2" | 5-3/8" |
| 7/32" | 0.2188 | 1-1/4" | 2-3/8" | 55/64" | 0.8594 | 3-1/2" | 5-1/2" |
| 15/64" | 0.2344 | 1-5/16" | 2-7/16" | 7/8" | 0.875 | 3-1/2" | 5-1/2" |
| 1/4" | 0.25 | 1-3/8" | 2-1/2" | 57/64" | 0.8906 | 3-5/8" | 5-5/8" |
| 17/64" | 0.2656 | 1-7/16" | 2-5/8" | 29/32" | 0.9062 | 3-5/8" | 5-5/8" |
| 9/32" | 0.2813 | 1-1/2" | 2-11/16" | 59/64" | 0.9219 | 3-3/4" | 5-3/4" |
| 19/64" | 0.2969 | 1-9/16" | 2-3/4" | 15/16" | 0.9375 | 3-3/4" | 5-3/4" |
| 5/16" | 0.3125 | 1-5/8" | 2-13/16" | 61/64" | 0.9531 | 3-7/8" | 5-7/8" |
| 21/64" | 0.3281 | 1-11/16" | 2-15/16" | 31/32" | 0.9688 | 3-7/8" | 5-7/8" |
| 11/32" | 0.3438 | 1-11/16" | 3" | 63/64" | 0.9844 | 4" | 6" |
| 23/64" | 0.3594 | 1-3/4" | 3-1/16" | 1" | 1 | 4" | 6" |
| 3/8" | 0.375 | 1-13/16" | 3-1/8" | 1-1/64" | 1.0156 | 4" | 6" |
| 25/64" | 0.3906 | 1-7/8" | 3-1/4" | 1-1/32" | 1.0312 | 4" | 6-1/4" |
| 13/32" | 0.4062 | 1-15/16" | 3-5/16" | 1-3/64" | 1.0469 | 4" | 6-1/4" |
| 27/64" | 0.4219 | 2" | 3-3/8" | 1-1/16" | 1.0625 | 4" | 6-1/4" |
| 7/16" | 0.4375 | 2-1/16" | 3-7/16" | 1-5/64" | 1.0781 | 4" | 6-1/4" |
| 29/64" | 0.4531 | 2-1/8" | 3-9/16" | 1-3/32" | 1.0938 | 4" | 6-1/4" |
| 15/32" | 0.4688 | 2-1/8" | 3-5/8" | 1-7/64" | 1.1094 | 4" | 6-1/4" |
| 31/64" | 0.4844 | 2-3/16" | 3-11/16" | 1-1/8" | 1.125 | 4" | 6-3/8" |
| 1/2" | 0.5 | 2-1/4" | 3-3/4" | 1-9/64" | 1.1406 | 4" | 6-3/8" |
| 33/64" | 0.5156 | 2-3/8" | 3-7/8" | 1-5/32" | 1.1562 | 4-1/4" | 6-5/8" |
| 17/32" | 0.5312 | 2-3/8" | 3-7/8" | 1-11/64" | 1.1719 | 4-1/4" | 6-5/8" |
| 35/64" | 0.5469 | 2-1/2" | 4" | 1-3/16" | 1.1875 | 4-1/4" | 6-5/8" |
| 9/16" | 0.5625 | 2-1/2" | 4" | 1-1/4" | 1.25 | 4-3/8" | 6-3/4" |
| 37/64" | 0.5781 | 2-5/8" | 4-1/8" | 1-9/32" | 1.2813 | 4-3/8" | 7" |
| 19/32" | 0.5938 | 2-5/8" | 4-1/8" | 1-5/16" | 1.3125 | 4-3/8" | 7" |
| 39/64" | 0.6094 | 2-3/4" | 4-1/4" | 1-3/8" | 1.375 | 4-1/2" | 7-1/8" |
| 5/8" | 0.625 | 2-3/4" | 4-1/4" | 1-13/32" | 1.4062 | 4-3/4" | 7-3/8" |
| 41/64" | 0.6406 | 2-7/8" | 4-1/2" | 1-7/16" | 1.4375 | 4-3/4" | 7-3/8" |
| 21/32" | 0.6562 | 2-7/8" | 4-1/2" | 1-1/2" | 1.5 | 4-7/8" | 7-1/2" |
| 43/64" | 0.6719 | 2-7/8" | 4-5/8" | 2" | 2 | 5-5/8" | 8-1/2" |
Numbered (Wire Gauge) Screw Machine Drill Lengths
| Drill Size | Decimal (in) | Flute (in) | Overall (in) | Drill Size | Decimal (in) | Flute (in) | Overall (in) |
|---|---|---|---|---|---|---|---|
| 1 | 0.228 | 1-5/16" | 2-7/16" | 31 | 0.12 | 7/8" | 1-7/8" |
| 2 | 0.221 | 1-5/16" | 2-7/16" | 32 | 0.116 | 7/8" | 1-7/8" |
| 3 | 0.213 | 1-1/4" | 2-3/8" | 33 | 0.113 | 7/8" | 1-7/8" |
| 4 | 0.209 | 1-1/4" | 2-3/8" | 34 | 0.111 | 7/8" | 1-7/8" |
| 5 | 0.2055 | 1-1/4" | 2-3/8" | 35 | 0.11 | 7/8" | 1-7/8" |
| 6 | 0.204 | 1-1/4" | 2-3/8" | 36 | 0.1065 | 13/16" | 1-13/16" |
| 7 | 0.201 | 1-3/16" | 2-1/4" | 37 | 0.104 | 13/16" | 1-13/16" |
| 8 | 0.199 | 1-3/16" | 2-1/4" | 38 | 0.1015 | 13/16" | 1-13/16" |
| 9 | 0.196 | 1-3/16" | 2-1/4" | 39 | 0.0995 | 13/16" | 1-13/16" |
| 10 | 0.1935 | 1-3/16" | 2-1/4" | 40 | 0.098 | 13/16" | 1-13/16" |
| 11 | 0.191 | 1-3/16" | 2-1/4" | 41 | 0.096 | 13/16" | 1-13/16" |
| 12 | 0.189 | 1-3/16" | 2-1/4" | 42 | 0.0935 | 3/4" | 1-3/4" |
| 13 | 0.185 | 1-1/8" | 2-3/16" | 43 | 0.089 | 3/4" | 1-3/4" |
| 14 | 0.182 | 1-1/8" | 2-3/16" | 44 | 0.086 | 3/4" | 1-3/4" |
| 15 | 0.18 | 1-1/8" | 2-3/16" | 45 | 0.082 | 3/4" | 1-3/4" |
| 16 | 0.177 | 1-1/8" | 2-3/16" | 46 | 0.081 | 3/4" | 1-3/4" |
| 17 | 0.173 | 1-1/8" | 2-3/16" | 47 | 0.0785 | 11/16" | 1-11/16" |
| 18 | 0.1695 | 1-1/16" | 2-1/8" | 48 | 0.076 | 11/16" | 1-11/16" |
| 19 | 0.166 | 1-1/16" | 2-1/8" | 49 | 0.073 | 11/16" | 1-11/16" |
| 20 | 0.161 | 1-1/16" | 2-1/8" | 50 | 0.07 | 11/16" | 1-11/16" |
| 21 | 0.159 | 1-1/16" | 2-1/8" | 51 | 0.067 | 11/16" | 1-11/16" |
| 22 | 0.157 | 1-1/16" | 2-1/8" | 52 | 0.0635 | 11/16" | 1-11/16" |
| 23 | 0.154 | 1" | 2-1/16" | 53 | 0.0595 | 5/8" | 1-5/8" |
| 24 | 0.152 | 1" | 2-1/16" | 54 | 0.055 | 5/8" | 1-5/8" |
| 25 | 0.1495 | 1" | 2-1/16" | 55 | 0.052 | 5/8" | 1-5/8" |
| 26 | 0.147 | 1" | 2-1/16" | 56 | 0.0465 | 1/2" | 1-3/8" |
| 27 | 0.144 | 1" | 2-1/16" | 57 | 0.043 | 1/2" | 1-3/8" |
| 28 | 0.1405 | 15/16" | 1-15/16" | 58 | 0.042 | 1/2" | 1-3/8" |
| 29 | 0.136 | 15/16" | 1-15/16" | 59 | 0.041 | 1/2" | 1-3/8" |
| 30 | 0.1285 | 15/16" | 1-15/16" | 60 | 0.04 | 1/2" | 1-3/8" |
Letter Screw Machine Drill Lengths
| Drill Size | Decimal (in) | Flute (in) | Overall (in) | Drill Size | Decimal (in) | Flute (in) | Overall (in) |
|---|---|---|---|---|---|---|---|
| A | 0.234 | 1-5/16" | 2-7/16" | N | 0.302 | 1-5/8" | 2-13/16" |
| B | 0.238 | 1-3/8" | 2-1/2" | O | 0.316 | 1-11/16" | 2-15/16" |
| C | 0.242 | 1-3/8" | 2-1/2" | P | 0.323 | 1-11/16" | 2-15/16" |
| D | 0.246 | 1-3/8" | 2-1/2" | Q | 0.332 | 1-11/16" | 3" |
| E | 0.25 | 1-3/8" | 2-1/2" | R | 0.339 | 1-11/16" | 3" |
| F | 0.257 | 1-7/16" | 2-5/8" | S | 0.348 | 1-3/4" | 3-1/16" |
| G | 0.261 | 1-7/16" | 2-5/8" | T | 0.358 | 1-3/4" | 3-1/16" |
| H | 0.266 | 1-1/2" | 2-11/16" | U | 0.368 | 1-13/16" | 3-1/8" |
| I | 0.272 | 1-1/2" | 2-11/16" | V | 0.377 | 1-7/8" | 3-1/4" |
| J | 0.277 | 1-1/2" | 2-11/16" | W | 0.386 | 1-7/8" | 3-1/4" |
| K | 0.281 | 1-1/2" | 2-11/16" | X | 0.397 | 1-15/16" | 3-5/16" |
| L | 0.29 | 1-9/16" | 2-3/4" | Y | 0.404 | 1-15/16" | 3-5/16" |
| M | 0.295 | 1-9/16" | 2-3/4" | Z | 0.413 | 2" | 3-3/8" |
Frequently Asked Questions About Screw Machine Drill Bits
What is a screw machine drill bit?
A screw machine drill bit, also called a stub length drill, is a shorter, more rigid twist drill designed for applications where compact tool length and reduced deflection are important.
What is the difference between screw machine and jobber length drill bits?
Screw machine drills have shorter flutes and shorter overall lengths than comparable jobber length drills. Their compact construction is useful for limited spindle clearance and can improve rigidity, while jobber drills generally offer more reach.
What are the advantages of stub length drill bits?
The shorter length helps limit flexing and vibration, making stub drills useful for accurate hole starting, machine setups, and confined spaces. Performance also depends on the material, machine, workholding, and cutting conditions.
Should I choose HSS or cobalt stub drills?
High Speed Steel (HSS) is a versatile choice for general drilling applications. Cobalt drills offer increased hot hardness and are often preferred for tougher materials such as stainless steel. Select the appropriate drill geometry and cutting parameters for the workpiece.
How do I determine the flute length and overall length of a stub drill?
Find the fractional, number, or letter drill size in the chart and read across to its flute length and overall length. Use the specific product listing for dimensions when your application has strict clearance or depth requirements.