WRENCH SIZE REFERENCE
Wrench Size Chart
Compare metric and SAE wrench sizes, match bolt diameters to the correct wrench, and check near-equivalent sizes with ISO-based tolerance guidance.
WRENCH SIZE BASICS
How to Read a Wrench Size Chart
Wrench size is the distance across two opposite flat sides of a hex head. Measure flat to flat — not corner to corner — before matching the fastener to a metric or SAE wrench size.
THE KEY DIMENSION
What Does A/F Mean?
A/F
Across Flats
A/F
Measure Flat to Flat
A/F is measured perpendicular to two opposite flat faces of the hex head. This dimension determines the nominal wrench opening.
Do not measure corner to corner.
The corner-to-corner dimension of a hex head is roughly 15% larger and can send you several sizes up the chart.
METRIC
10 · 13 · 17
Opening size is marked directly in millimetres.
SAE
3/8″ · 1/2″ · 3/4″
Opening size is marked as a fraction of an inch.
5-STEP CHECK
How to Measure a Fastener
Use the head dimension to identify the correct wrench opening before applying load.
01
Look for a Stamped Size
Check the fastener head for existing markings, but confirm whether the marking refers to the thread, grade or head size.
02
Measure Across the Flats
Use a caliper across two opposite flat faces. Record the measurement in millimetres for easy comparison.
03
Match the Nominal Size
Compare the measured width with the nearest nominal wrench size and account for ISO or older DIN head dimensions where applicable.
04
Test-Fit the Wrench
The correct wrench should slide fully onto the hex head with minimal clearance and seat squarely on the flats.
05
Stop If the Tool Rocks
Side-to-side movement indicates excessive clearance. Under load, an oversized opening can walk across the flats and round the fastener head.
SIZE REFERENCE
Wrench Size Chart: Metric & SAE
Compare SAE and metric wrench sizes, match bolt diameters to the correct opening, and identify the ISO/DIN head-size differences that commonly cause incorrect tool selection.
EXACT CONVERSION
1 in = 25.4 mm
WRENCH DIMENSION
A/F · Across Flats
CLOSE PAIR
3/4″ ≈ 19 mm
CHECK FIRST
ISO vs Older DIN
01
CONVERSION TABLE
SAE to Metric Wrench Sizes
Inch sizes converted using 1 inch = 25.4 mm exactly. Metric values are rounded to two decimal places.
| SAE (inch) | Decimal Inch | Metric (mm) |
|---|---|---|
| 5/32″ | 0.15625 | 3.97 mm |
| 3/16″ | 0.1875 | 4.76 mm |
| 1/4″ | 0.25 | 6.35 mm |
| 5/16″ | 0.3125 | 7.94 mm |
| 3/8″ | 0.375 | 9.53 mm |
| 7/16″ | 0.4375 | 11.11 mm |
| 1/2″ | 0.5 | 12.70 mm |
| 9/16″ | 0.5625 | 14.29 mm |
| 5/8″ | 0.625 | 15.88 mm |
| 11/16″ | 0.6875 | 17.46 mm |
| 3/4″ | 0.75 | 19.05 mm |
| 13/16″ | 0.8125 | 20.64 mm |
| 7/8″ | 0.875 | 22.23 mm |
| 15/16″ | 0.9375 | 23.81 mm |
| 1″ | 1.0 | 25.40 mm |
| 1-1/8″ | 1.125 | 28.58 mm |
| 1-1/4″ | 1.25 | 31.75 mm |
| 1-1/2″ | 1.5 | 38.10 mm |
| 1-3/4″ | 1.75 | 44.45 mm |
| 2″ | 2.0 | 50.80 mm |
02
METRIC FASTENER LOOKUP
Metric Thread to Wrench Size
Thread diameter and wrench opening are different dimensions. The required opening depends on the fastener head standard.
| Metric Thread | ISO Head A/F | Older DIN Head A/F | Status |
|---|---|---|---|
| M3 | 5.5 mm | 5.5 mm | Same |
| M4 | 7 mm | 7 mm | Same |
| M5 | 8 mm | 8 mm | Same |
| M6 | 10 mm | 10 mm | Same |
| M7 | 11 mm | 11 mm | Same |
| M8 | 13 mm | 13 mm | Same |
| M10 | 16 mm | 17 mm | Check |
| M12 | 18 mm | 19 mm | Check |
| M14 | 21 mm | 22 mm | Check |
| M16 | 24 mm | 24 mm | Same |
| M18 | 27 mm | 27 mm | Same |
| M20 | 30 mm | 30 mm | Same |
| M22 | 32 mm | 32 mm | Same |
| M24 | 36 mm | 36 mm | Same |
| M27 | 41 mm | 41 mm | Same |
| M30 | 46 mm | 46 mm | Same |
| M33 | 50 mm | 50 mm | Same |
| M36 | 55 mm | 55 mm | Same |
WHY TWO SIZES?
The Same Metric Thread Can Use a Different Wrench
M10, M12 and M14 are the sizes most likely to cause confusion. Older DIN head dimensions and current ISO dimensions differ by 1 mm across the flats.
M10
ISO
16 mm
→
Older DIN
17 mm
M12
ISO
18 mm
→
Older DIN
19 mm
M14
ISO
21 mm
→
Older DIN
22 mm
03
SAE FASTENER LOOKUP
SAE Bolt Diameter to Wrench Size
Standard hex-series reference for matching common SAE bolt diameters with wrench openings.
| Bolt Diameter | Wrench Size | Decimal Inch | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1/4″ | 7/16″ | 0.4375 | ||||||||||||||||||||||
| 5/16″ | 1/2″ | 0.5 | ||||||||||||||||||||||
| 3/8″ |
9/16″ |
0.5625 |
7/16″ |
5/8″ |
0.625 |
1/2″ |
3/4″ |
0.75 |
9/16″ |
13/16″ |
0.8125 |
5/8″ |
15/16″ |
0.9375 |
3/4″ |
1-1/8″ |
1.125 |
7/8″ |
1-5/16″ |
1.3125 |
1″ |
1-1/2″ |
1.5 |
|
VERIFY BEFORE YOU SPECIFY
A nominal chart value is a starting point,
not a guarantee of fit.
Head dimensions depend on the applicable fastener standard and head series. Confirm the standard and measure the actual width across flats before applying torque, especially when working with older equipment or mixed metric fastener inventories.
BEFORE YOU APPLY TORQUE
Head Sizes Vary. Measure Before You Torque.
Wrench charts show nominal dimensions. The actual width across flats can change with the head standard, surface coating and condition of the fastener.
NOMINAL ≠ ACTUAL
A Chart Gives You the Starting Size
A wrench size is a nominal opening matched to a nominal fastener head. Real fasteners can move away from that dimension before the wrench ever reaches the joint.
CHART VALUE
Nominal
Standard head dimension
→
ACTUAL FASTENER
Measure
Real width across flats
If the fastener is critical, measure it.
If it is coated, worn, painted or corroded, measure it again before selecting the wrench.
01
Head Standard & Series
STANDARDISO, DIN and ANSI can define different head dimensions for the same thread size. Standard hex and heavy hex can also require different wrench openings.
02
Coating Thickness
FINISHHot-dip galvanizing adds measurable material to the fastener surface. A coated head or nut may therefore require more clearance than the equivalent plain fastener.
Plain
Coated
Heavy Coating
03
Condition & Reuse
CONDITIONWear, rounded corners, paint and corrosion move the head away from its nominal geometry. No standard size chart can predict those changes.
PRACTICAL RULE
Use the chart to identify the nominal size.
Use the actual fastener to confirm the fit.
Standards define tolerance bands rather than one perfect physical dimension. A wrench that fits loosely enough to rock under load is not the correct choice simply because its nominal size appears close.
FINAL CHECK
Measure A/F
BUYER RANGE PLANNING
What Wrench Sizes Should Your Range Carry?
Selecting a wrench range is different from matching one fastener. For importers, distributors and private-label programs, the real question is which sizes deserve space in the opening assortment.
METRIC CORE
Build Around the Sizes That Actually Move
6–24
mm
A practical general-purpose metric program spans approximately 6 mm to 24 mm, but demand is not distributed evenly across that range.
10
mm
13
mm
17
mm
19
mm
High-frequency core sizes
These sizes account for a disproportionate share of everyday use, replacement demand and reorder activity in a general metric wrench program.
COMMONLY OMITTED
The Sizes Basic Sets Skip
Lower-priced sets frequently remove sizes to reduce piece count and hit a target retail price. Two metric sizes deserve particular attention.
OFTEN SKIPPED
16
mm
+
OFTEN SKIPPED
18
mm
WHY THEY MATTER
These sizes became more important with the change from older DIN head dimensions to current ISO dimensions. Markets with older and newer equipment in service may need both sides of the size pairs.
SAE CORE RANGE
Start With the Sizes That Cover General North American Work
A core SAE program typically concentrates on 1/4″ through 3/4″. Larger sizes can be treated as supplementary inventory rather than carrying the same opening-order depth.
1/4″
Core Start
1/2″
Core
3/4″
Core End
1″+
Supplementary
PRODUCT CONFIGURATION
Size Progression Sets the Price Point
The same manufacturing platform can support different retail positions depending on size progression and wrench-head configuration.
01
COMPLETE RANGE
Full 1 mm Progression
Broader size coverage with fewer gaps for professional users and markets where equipment generations are mixed.
Higher Piece Count
02
VALUE RANGE
Selected Size Progression
Remove lower-frequency sizes to reduce piece count, packaging volume and the final retail price.
Lower Entry Price
03
TOOL CONFIGURATION
6-Point or 12-Point
Head geometry creates another product tier and changes the application positioning even when the nominal size spread remains the same.
Different User Positioning
RANGE-PLANNING CONSEQUENCE
Mixed DIN and ISO Markets Need Both Sides of the Pair
If installed equipment spans the DIN-to-ISO transition, carrying only one size from each pair can create avoidable fit complaints and returns.
PAIR 01
16
mm
+
17
mm
PAIR 02
18
mm
+
19
mm
SMALL SKU ADDITION
Fewer Fit Complaints
Better coverage of mixed equipment fleets
VERIFY BEFORE YOU CLAIM
Match the specification to the exact SKU and target market.
Wrench materials, hardness, dimensions and standards conformance are product- and market-specific. Confirm the applicable standard, certificate, test report and SKU before making a compliance claim.
RANGE INPUTS
Sizes · Set · Price
Frequently Asked Questions (FAQs)
Find answers to common questions about our hand tools, their care, and usage. If you need additional information, our customer support team is ready to assist you.
Why doesn’t a 10 mm wrench fit an M10 bolt?
Because the wrench size is the head width across flats, not the thread diameter. An M10 hex head is nominally 16 mm across the flats under ISO sizing or 17 mm under the older DIN sizing, so it takes a 16 mm or 17 mm wrench. The number in the thread designation describes the thread, not the head.
What size wrench do I need for a 10 mm bolt?
There is usually no such thing as a 10 mm bolt, which is the source of the confusion. If you mean an M10 metric fastener, the wrench is 16 mm or 17 mm depending on the head standard. If you mean an SAE bolt with a 10 mm head, measure across the flats and use a 10 mm wrench.
Is a 13 mm wrench the same as a 1/2 inch?
No. A 1/2″ head measures 12.70 mm across the flats, so a 13 mm wrench is 0.30 mm larger. It will often go on and turn a 1/2″ fastener for light work. The reverse does not hold. A 1/2″ wrench measures 12.70 mm and will not fit a 13 mm head.
Are metric and SAE wrenches interchangeable?
Only in a few specific pairs and only in one direction. A wrench slightly larger than the head may work for light hand-tightening, and a wrench smaller than the head will not fit at all. Never substitute on high-torque, seized, rusted or galvanized fasteners, where a loose fit will round the head.
How do I measure a bolt to find the wrench size?
Measure across the flats of the hex head with a caliper, flat side to flat side, never corner to corner. Match the millimetre figure to the chart above, check whether the head follows ISO or the older DIN sizing, then test-fit. A correct wrench seats fully with no side-to-side movement.
What wrench sizes should be in a basic set?
A metric set should span 6 mm to 24 mm with 10, 13, 17 and 19 mm as the high-use sizes, and should ideally include both 16 mm and 17 mm and both 18 mm and 19 mm if older equipment is in service. An SAE set should cover 1/4″ to 3/4″. Anything above 1″ is usually better bought individually than carried in a set.