What are Allen Keys?
Allen keys, also called hex keys, L-keys, or Allen wrenches—are six-sided L-shaped tools used to drive socket (hex) fasteners. They’re essential for assembling machinery, bikes, furniture, and for general shop work. This page covers common styles, how to choose the right key, and complete size specifications for SAE, metric, and Torx/star tamper-proof L-keys.
Long Arm vs. Short Arm Allen Keys
Long Arm Allen Keys
- Extra reach and leverage for deep or hard-to-access fasteners
- Higher torque with less effort; easier to spin fasteners quickly
- Often available with a ball end for up to ~25° entry angle
- Offered in both SAE (inch) and metric sizes
Short Arm Allen Keys
- Compact for tight clearances; better control in confined spaces
- Shorter throw gives a secure fit and reduces rounding risk
- Great as a dedicated “stubby” for panels, fixtures, and cabinetry
Materials & Durability
- Black alloy steel for strength, toughness, and long service life
- Precision-machined tips for accurate fit and reduced cam-out
- Heat treated and wear-resistant for daily professional use
- Available finishes that help resist corrosion in demanding environments
Benefits of Allen Keys
- Simple, compact tools that cover a huge range of assembly and repair tasks
- Less likely than slotted/Phillips to slip and mar fasteners
- Flat sides resist rolling; easy to pocket or keep in a kit
Allen Wrench Sets & L-Keys
Choose individual keys for common sizes or grab complete hex key sets for shop coverage. Options include SAE, metric, long-arm, short-arm, ball-end, and T-handle styles for extra control and faster spinning. Multi-piece sets keep sizes organized and ready to go.
Allen Key Specifications
Short Arm SAE Hex Key Specifications
| Hex Allen Key Sizes | Width Across Flats | Length of Long Arm | Length of Short Arm |
|---|---|---|---|
| 0.028" | Max 0.0280 - Min 0.0275 | 1.219" | 0.219" |
| 0.035" | Max 0.0350 - Min 0.0345 | 1.219" | 0.344" |
| 0.050" | Max 0.050 - Min 0.049 | 1.656" | 0.531" |
| 1/16" | Max 0.0625 - Min 0.0615 | 1.75" | 0.562" |
| 5/64" | Max 0.0781 - Min 0.0771 | 1.875" | 0.609" |
| 3/32" | Max 0.0937 - Min 0.0927 | 2" | 0.656" |
| 7/64" | Max 0.1093 - Min 0.1077 | 2.125" | 0.703" |
| 1/8" | Max 0.1250 - Min 0.1235 | 2.25" | 0.75" |
| 9/64" | Max 0.1406 - Min 0.1391 | 2.375" | 0.796" |
| 5/32" | Max 0.1562 - Min 0.1547 | 2.5" | 0.844" |
| 3/16" | Max 0.1875 - Min 0.1860 | 2.75" | 0.938" |
| 7/32" | Max 0.2187 - Min 0.2172 | 3" | 1.031" |
| 1/4" | Max 0.250 - Min 0.248 | 3.25" | 1.125" |
| 5/16" | Max 0.3125 - Min 0.3110 | 3.75" | 1.25" |
| 3/8" | Max 0.375 - Min 0.373 | 4.25" | 1.375" |
| 7/16" | Max 0.4375 - Min 0.4355 | 4.75" | 1.5" |
| 1/2" | Max 0.5000 - Min 0.4975 | 5.25" | 1.625" |
| 9/16" | Max 0.5625 - Min 0.5600 | 5.75" | 1.75" |
| 5/8" | Max 0.6250 - Min 0.6225 | 6.25" | 1.875" |
| 3/4" | Max 0.750 - Min 0.747 | 7.25" | 2.125" |
| 7/8" | Max 0.875 - Min 0.872 | 8.25" | 2.375" |
| 1" | Max 1.000 - Min 0.997 | 9.25" | 2.65" |
Long Arm SAE Hex Key Specifications
| Hex Allen Key Sizes | Width Across Flats | Length of Long Arm | Length of Short Arm |
|---|---|---|---|
| 0.050" | Max 0.050 - Min 0.049 | 2.844" | 0.531" |
| 1/16" | Max 0.0625 - Min 0.0615 | 3" | 0.562" |
| 5/64" | Max 0.0781 - Min 0.0771 | 3.188" | 0.609" |
| 3/32" | Max 0.0937 - Min 0.0927 | 3.375" | 0.656" |
| 7/64" | Max 0.1093 - Min 0.1077 | 3.562" | 0.703" |
| 1/8" | Max 0.1250 - Min 0.1235 | 3.75" | 0.75" |
| 9/64" | Max 0.1406 - Min 0.1391 | 3.937" | 0.796" |
| 5/32" | Max 0.1562 - Min 0.1547 | 4.125" | 0.844" |
| 3/16" | Max 0.1875 - Min 0.1860 | 4.5" | 0.938" |
| 7/32" | Max 0.2187 - Min 0.2172 | 4.875" | 1.031" |
| 1/4" | Max 0.250 - Min 0.248 | 5.25" | 1.125" |
| 5/16" | Max 0.3125 - Min 0.3110 | 6" | 1.25" |
| 3/8" | Max 0.375 - Min 0.373 | 6.75" | 1.375" |
| 7/16" | Max 0.4375 - Min 0.4355 | 7.5" | 1.5" |
| 1/2" | Max 0.5000 - Min 0.4975 | 8.25" | 1.625" |
| 9/16" | Max 0.5625 - Min 0.5600 | 9" | 1.75" |
| 5/8" | Max 0.6250 - Min 0.6225 | 9.75" | 1.875" |
| 3/4" | Max 0.750 - Min 0.747 | 11.25" | 2.125" |
| 7/8" | Max 0.875 - Min 0.872 | 12.75" | 2.375" |
| 1" | Max 1.000 - Min 0.997 | 14.25" | 2.65" |
Short Arm Metric Hex Key Specifications
| Hex Allen Key Sizes | Width Across Flats | Length of Long Arm | Length of Short Arm |
|---|---|---|---|
| 0.9M | Max 0.899 - Min 0.876 | Max 34M - Min 28M | Max 11M - Min 6M |
| 1.3M | Max 1.270 - Min 1.244 | Max 44M - Min 39M | Max 16M - Min 11M |
| 1.5M | Max 1.50 - Min 1.47 | Max 45M - Min 43M | Max 14M - Min 13M |
| 2M | Max 2.00 - Min 1.97 | Max 50M - Min 48M | Max 16M - Min 15M |
| 2.5M | Max 2.50 - Min 2.47 | Max 56M - Min 53M | Max 18M - Min 17M |
| 3M | Max 3.00 - Min 2.96 | Max 63M - Min 60M | Max 20M - Min 18M |
| 4M | Max 4.00 - Min 3.96 | Max 70M - Min 66M | Max 25M - Min 23M |
| 5M | Max 5.00 - Min 4.96 | Max 80M - Min 76M | Max 28M - Min 26M |
| 6M | Max 6.00 - Min 5.95 | Max 90M - Min 86M | Max 32M - Min 30M |
| 8M | Max 8.00 - Min 7.95 | Max 100M - Min 95M | Max 36M - Min 34M |
| 10M | Max 10.00 - Min 9.95 | Max 112M - Min 106M | Max 40M - Min 38M |
| 12M | Max 12.00 - Min 11.95 | Max 125M - Min 119M | Max 45M - Min 43M |
| 14M | Max 14.00 - Min 13.95 | Max 140M - Min 133M | Max 56M - Min 53M |
| 17M | Max 17.00 - Min 16.93 | Max 160M - Min 152M | Max 63M - Min 60M |
| 19M | Max 19.00 - Min 18.93 | Max 280M - Min 271M | Max 70M - Min 67M |
Long Arm Metric Hex Key Specifications
| Hex Allen Key Sizes | Width Across Flats | Length of Long Arm | Length of Short Arm |
|---|---|---|---|
| 1.5M | Max 1.50 - Min 1.47 | Max 78M - Min 76M | Max 14M - Min 13M |
| 2M | Max 2.00 - Min 1.97 | Max 83M - Min 81M | Max 16M - Min 15M |
| 2.5M | Max 2.50 - Min 2.47 | Max 90M - Min 87M | Max 18M - Min 17M |
| 3M | Max 3.00 - Min 2.96 | Max 100M - Min 97M | Max 20M - Min 18M |
| 4M | Max 4.00 - Min 3.96 | Max 106M - Min 102M | Max 25M - Min 23M |
| 5M | Max 5.00 - Min 4.96 | Max 118M - Min 114M | Max 28M - Min 26M |
| 6M | Max 6.00 - Min 5.95 | Max 140M - Min 136M | Max 32M - Min 30M |
| 7M | Max 7.00 - Min 6.97 | Max 145M - Min 140M | Max 36M - Min 34M |
| 8M | Max 8.00 - Min 7.95 | Max 160M - Min 155M | Max 36M - Min 34M |
| 10M | Max 10.00 - Min 9.95 | Max 170M - Min 164M | Max 40M - Min 38M |
Torx / Star Tamper Proof L Key Specifications
| Drive Size: | Length of Short Arm: | Length of Long Arm: |
|---|---|---|
| T-6 | 0.50" | 1.65" |
| T-7 | 0.55" | 1.75" |
| T-8 | 0.60" | 1.85" |
| T-9 | 0.65" | 2.00" |
| T-10 | 0.70" | 2.10" |
| T-15 | 0.75" | 2.20" |
| T-20 | 0.80" | 2.35" |
| T-25 | 0.85" | 2.50" |
| T-27 | 0.95" | 2.75" |
| T-30 | 1.05" | 3.00" |
| T-45 | 1.25" | 3.75" |
| T-50 | 1.35" | 4.25" |
| T-55 | 1.50" | 4.75" |
How to Choose the Right Allen Key
- Match the fastener: pick SAE or metric to fit the socket precisely.
- Select length: short arm for tight spaces; long arm for reach and torque/ball-end access.
- Pick handle style: standard L-key for compact carry or T-handle for speed and control.
- Consider duty cycle: heavy daily use favors premium alloy steel sets with organized holders.
Maintenance & Care
- Keep keys clean and dry; store in holders to prevent loss
- Inspect tips regularly; replace worn keys to protect fasteners
- Use the correct size to avoid rounding sockets
Allen Keys FAQ
What’s the difference between long-arm and short-arm keys?
Long-arm keys provide greater leverage and reach (often with ball ends). Short-arm keys are compact for confined spaces and offer better control near the head.
Do I need SAE or metric?
Match the fastener system on your project. Mixing systems can round the socket—use SAE for inch fasteners and metric for metric hardware.
When should I choose a ball-end key?
Use ball-end keys when you need to approach at an angle. For final high-torque break-loose or final tightening, switch to a straight-cut tip.
What are T-handle hex keys good for?
T-handles improve grip and speed for repetitive assembly and provide more comfortable torque application.