Hex Key Sizes Chart for Common Bolts
Hex key sizes come in metric and SAE families, and this guide charts the sizes 4 sets state, with tips for measuring a bolt before turning.
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The bolt head stares back from inside the wheel well, a small socket that no wrench in the tray fits, and the job stops until the right hex key turns up. Hex key sizes come in metric and SAE families, and the right key is the one that matches the socket exactly, with no wobble and no rounding of the corners.
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Below: both families, a chart of the sizes the listings state, how to measure a bolt, and the gear that covers the chart.
Bondhus 20199 Balldriver L-Wrench DoublePK
A set of ball-end L-wrenches spanning 1.5 to 10 mm and 0.050 to 3/8 in, with a full lifetime warranty.
Pros
- Ball ends work at up to 25 degrees
- Metric 1.5 to 10 mm plus SAE 0.050 to 3/8 in
- Full lifetime warranty
- Ball ends turn screws without constant repositioning
Cons
- No storage case is listed
- No size markings are stated
- Heavier than the Skil tool at 2.0 lb
- L-wrenches need hand turning, no powered drive
Amazon Basics Hex Key Allen Wrench, Long Arm
A 26-piece long-arm set in metric and standard sizes, with ball ends, chrome-vanadium steel and 2 hinged storage cases.
Pros
- 26 pieces in metric and standard sizes
- Ball ends allow entry up to 25 degrees
- Long arms add reach and leverage
- 2 hinged cases with clear size markings
Cons
- 1-year limited warranty, shorter than lifetime cover
- Long arms need clearance around the fastener
- No powered drive for repetitive fastening
- 26 pieces across 2 cases to keep organized
Klein Tools 652216HEXL Long Hex Bit Socket Set
A 16-piece set of long hex bit sockets in SAE 5/32 to 1/2 in and metric 4 to 12 mm, in a MODbox case.
Pros
- SAE 5/32 to 1/2 in and metric 4 to 12 mm
- Long bits reach into tight spaces
- Knurling grips when starting fasteners by hand
- Bold stamped size markings
Cons
- No warranty term is stated beyond calling the vendor
- Sockets need a ratchet or driver to turn
- SAE sizes start at 5/32 in and metric at 4 mm, so smaller sizes need another set
- 16 pieces, fewer sizes than the 26-piece set
Skil PWRCORE GO 4V Folding Hex Key with 11-Pc. Bit
A 4V powered folding hex key with an 11-piece bit set, a locking head and an LED work light, recharged by USB-C.
Pros
- Push-button forward and reverse drive
- Head locks at 90, 135 or 180 degrees
- LED work light for low-light areas
- 11-piece bit set with onboard storage
Cons
- No warranty term is stated
- Hex bits only to H6, no larger sizes
- Onboard holder stores up to 5 bits, not the full set
- Needs USB-C charging before use
Hex key sizes: metric and SAE
A metric key is sized in millimeters and an SAE key in fractions of an inch, so use the size the socket was made for, and read the markings on the key before turning. The chart below lists only the sizes each listing states. Where a listing gives a range, the chart shows the range; where it gives no range, the chart says so.
| Set | Metric sizes stated | SAE sizes stated |
|---|---|---|
| Bondhus DoublePK | 1.5 to 10 mm | 0.050 to 3/8 in |
| Amazon Basics 26-Piece | Metric and standard sizes, no range stated | Metric and standard sizes, no range stated |
| Klein 16-Piece Hex Set | 4 to 12 mm | 5/32 to 1/2 in |
| Skil Folding Hex Key | H2, H2.5, H3, H4, H5, H6 | No SAE hex sizes stated |
The Bondhus set spans both families in one purchase, while the Klein set pairs metric and SAE sizes in socket form. The Skil tool covers the small metric sizes only, so check the chart before reaching for it on a larger bolt.
How to measure a bolt for the right hex key
Read the socket before reaching for a key. Slide keys into the socket until one seats fully with no wobble: a key that rocks or turns loosely is the wrong size, and a key that will not enter is too large. On the Bondhus and Amazon Basics sets, a ball end lets the key enter at up to 25 degrees, which helps around obstructions, and the long arms on the Amazon Basics set add reach and leverage where the fastener sits deep. When the size marking has worn off, work through the set in order from the smallest key and stop at the one that seats without play.
The gear that covers the chart
Once the chart points to a size family, these 4 sets cover the measuring and turning: the Bondhus and Amazon Basics sets span both families, the Klein set turns hex fasteners with a ratchet, and the Skil tool powers the small sizes.
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FAQ: garage tools
What is the difference between metric and SAE hex keys?
Metric keys are sized in millimeters and SAE keys in fractions of an inch. The Bondhus set lists 1.5 to 10 mm and 0.050 to 3/8 in, and the Klein set lists 4 to 12 mm and 5/32 to 1/2 in, so both families appear in the sets here.
What hex key size fits a common bolt?
No one size fits every bolt: read the socket, then match the key to it. The chart above lists the sizes each set states, so check the socket against the chart before turning.
What does a ball end do on a hex key?
A ball end lets the key enter the socket at an angle, up to 25 degrees on the Amazon Basics and Bondhus sets, so the key reaches fasteners that sit behind obstructions. A straight end needs a straight approach, so use the ball end where the angle helps and the straight end where the key must sit square.
Do I need a powered hex key?
Not for every job. The Skil 4V tool drives hex screws with push-button forward and reverse, which suits furniture assembly and bike maintenance, while the manual sets cover the full size ranges here. A powered tool helps where the same small size turns again and again.
How do I keep hex key sizes readable?
Use the markings the maker puts on the keys and the case. The Amazon Basics set arrives in 2 hinged cases with dedicated slots and clear size markings, the Klein set has bold stamped size markings, and the Skil tool stores up to 5 bits onboard, so the bits in use stay with the tool.
Related: the best SAE hex key sets, the best metric hex key sets with a ball end, the best hex key sets for beginners and the engine and shop equipment hub.
