SOCKET SIZE REFERENCE
Socket Size Chart
Compare metric and SAE socket sizes in mm and inches, convert between systems, and match bolt and nut flats—not thread size—to the correct socket. Includes conversion tables, tolerances, and common near-equivalent sizes.
SOCKET SIZE BASICS
Socket Size vs Drive Size
A socket has two numbers: the hex opening that grips the fastener, and the square drive that connects to the ratchet. Socket size sets the fit. Drive size sets torque capacity. They are independent.
THE KEY DISTINCTION
Socket Size vs Drive Size
HEX
Socket Size
SOCKET SIZE
Hex Opening vs Square Drive
Socket size is the hex opening that grips the fastener, such as 13 mm. Drive size is the square end that connects to the ratchet, such as 3/8″. A socket is marked with both.
Do not measure corner to corner.
Corner-to-corner is roughly 15% larger and often suggests a socket size that does not exist.
SOCKET SIZE
10 · 13 · 17 mm
Hex opening marked in millimetres or fractional inches.
DRIVE SIZE
1/4″ · 3/8″ · 1/2″
Square end marked in inches, even on metric sockets.
5-STEP CHECK
How to Measure for Socket Size
Use the head dimension to identify the correct socket opening before applying load.
01
Look for a Stamped Size
Check the head for markings, but confirm whether it refers to thread, grade or head size.
02
Measure Across the Flats
Use a caliper flat side to flat side. Record in millimetres for easy comparison.
03
Match to the Chart
Take the nearest nominal size and check whether the fastener follows ISO or older DIN head sizing.
04
Test-Fit Before Torque
A correct socket seats fully on the head with no side-to-side movement.
05
Stop If It Rocks
Movement means the opening is too large. Under load it can slip and round the corners of the head.
SIZE REFERENCE
Socket Size Chart: Metric & SAE
Convert SAE and metric socket sizes, check exact millimetre equivalents, and identify near-swap pairs that fit—or fail— before applying torque.
EXACT CONVERSION
1 in = 25.4 mm
ROUNDING
2 decimal places
CLOSE PAIR
27 mm ≈ 1-1/16″
CHECK FIRST
32nd-step sizes
01
CONVERSION TABLE
SAE to Metric Socket Sizes Under 1 Inch
Inch sizes converted using 1 inch = 25.4 mm exactly. Metric values are rounded to two decimal places; the exact value is the unrounded product.
| SAE (inch) | Decimal Inch | Metric (mm) |
|---|---|---|
| 5/32″ | 0.15625 | 3.97 mm |
| 3/16″ | 0.1875 | 4.76 mm |
| 7/32″ | 0.21875 | 5.56 mm |
| 1/4″ | 0.25 | 6.35 mm |
| 9/32″ | 0.28125 | 7.14 mm |
| 5/16″ | 0.3125 | 7.94 mm |
| 11/32″ | 0.34375 | 8.73 mm |
| 3/8″ | 0.375 | 9.53 mm |
| 13/32″ | 0.40625 | 10.32 mm |
| 7/16″ | 0.4375 | 11.11 mm |
| 15/32″ | 0.46875 | 11.91 mm |
| 1/2″ | 0.5 | 12.70 mm |
| 17/32″ | 0.53125 | 13.49 mm |
| 9/16″ | 0.5625 | 14.29 mm |
| 19/32″ | 0.59375 | 15.08 mm |
| 5/8″ | 0.625 | 15.88 mm |
| 21/32″ | 0.65625 | 16.67 mm |
| 11/16″ | 0.6875 | 17.46 mm |
| 23/32″ | 0.71875 | 18.26 mm |
| 3/4″ | 0.75 | 19.05 mm |
| 25/32″ | 0.78125 | 19.84 mm |
| 13/16″ | 0.8125 | 20.64 mm |
| 27/32″ | 0.84375 | 21.43 mm |
| 7/8″ | 0.875 | 22.23 mm |
| 29/32″ | 0.90625 | 23.02 mm |
| 15/16″ | 0.9375 | 23.81 mm |
| 31/32″ | 0.96875 | 24.61 mm |
| 1″ | 1.0 | 25.40 mm |
02
CONVERSION TABLE
SAE to Metric Socket Sizes From 1 Inch Up
Same exact conversion and two-decimal rounding for larger inch sizes.
| SAE (inch) | Decimal Inch | Metric (mm) |
|---|---|---|
| 1-1/16″ | 1.0625 | 26.99 mm |
| 1-1/8″ | 1.125 | 28.58 mm |
| 1-3/16″ | 1.1875 | 30.16 mm |
| 1-1/4″ | 1.25 | 31.75 mm |
| 1-5/16″ | 1.3125 | 33.34 mm |
| 1-3/8″ | 1.375 | 34.93 mm |
| 1-7/16″ | 1.4375 | 36.51 mm |
| 1-1/2″ | 1.5 | 38.10 mm |
| 1-5/8″ | 1.625 | 41.28 mm |
| 1-3/4″ | 1.75 | 44.45 mm |
| 1-7/8″ | 1.875 | 47.63 mm |
| 2″ | 2.0 | 50.80 mm |
| 2-1/8″ | 2.125 | 53.98 mm |
| 2-1/4″ | 2.25 | 57.15 mm |
| 2-3/8″ | 2.375 | 60.33 mm |
| 2-1/2″ | 2.5 | 63.50 mm |
03
NEAR-SWAP REFERENCE
Which Metric and SAE Sockets Actually Fit
Some sizes sit close enough to be used interchangeably. The verdict column shows whether the metric socket is larger or smaller than the SAE fastener, and whether the pair is safe in practice.
| Metric Socket | Nearest SAE | SAE in mm | Gap | Socket vs Fastener | Verdict |
|---|---|---|---|---|---|
| 8 mm | 5/16″ | 7.94 mm | 0.06 mm | Larger | Fits well. Light duty is fine. |
| 10 mm | 3/8″ | 9.53 mm | 0.48 mm | Larger | Loose. Light duty only. |
| 11 mm | 7/16″ | 11.11 mm | 0.11 mm | Smaller | Will not fit. Use the 7/16″. |
| 12 mm | 15/32″ | 11.91 mm | 0.09 mm | Larger | Fits well. |
| 13 mm | 1/2″ | 12.70 mm | 0.30 mm | Larger | Fits. Light duty only. |
| 14 mm | 9/16″ | 14.29 mm | 0.29 mm | Smaller | Will not fit. Use the 9/16″. |
| 15 mm | 19/32″ | 15.08 mm | 0.08 mm | Smaller | Will not fit. Use the 19/32″. |
| 16 mm | 5/8″ | 15.88 mm | 0.13 mm | Larger | Fits well. |
| 17 mm | 11/16″ | 17.46 mm | 0.46 mm | Smaller | Will not fit. Use the 11/16″. |
| 18 mm | 11/16″ | 17.46 mm | 0.54 mm | Larger | Loose. Light duty only. |
| 19 mm | 3/4″ | 19.05 mm | 0.05 mm | Smaller on paper | Interchangeable in practice. The gap is inside the permitted opening tolerance of both parts. |
| 21 mm | 13/16″ | 20.64 mm | 0.36 mm | Larger | Loose. Light duty only. |
| 22 mm | 7/8″ | 22.23 mm | 0.23 mm | Smaller | Will not fit. Use the 7/8″. |
| 24 mm | 15/16″ | 23.81 mm | 0.19 mm | Larger | Fits well. |
| 25 mm | 1″ | 25.40 mm | 0.40 mm | Smaller | Will not fit. Use the 1″. |
| 27 mm | 1-1/16″ | 26.99 mm | 0.01 mm | Larger | Interchangeable in practice. The closest pair in the table. |
| 29 mm | 1-1/8″ | 28.58 mm | 0.43 mm | Larger | Loose. Light duty only. |
| 32 mm | 1-1/4″ | 31.75 mm | 0.25 mm | Larger | Fits. Light duty only. |
| 38 mm | 1-1/2″ | 38.10 mm | 0.10 mm | Smaller | Will not fit. Use the 1-1/2″. |
VERIFY BEFORE YOU SPECIFY
A nominal chart value is a starting point,
not a guarantee of fit.
The nearest-SAE column uses sizes common in SAE socket sets. Closer matches such as 23/32″ and 27/32″ are not routinely stocked and are excluded. Confirm which 32nd-step sizes your own sets carry, and check tolerance before applying torque.
FASTENER LOOKUP
Thread Size to Socket Size
Match metric thread designations and SAE bolt diameters to the correct head width across flats, including the ISO and older DIN differences that catch people out.
METRIC SYSTEM
Thread ≠ Head Size
SAE SYSTEM
Bolt ≠ Socket Size
WATCH FOR
M10 · M12 · M14
SAE STANDARD
ASME B18.2.1
01
METRIC FASTENER LOOKUP
Metric Thread Sizes to Hex Head Size
Metric fasteners are designated by thread size, such as M10. The socket size is the head width across flats, a separate dimension set by the 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 Socket
Older DIN head dimensions and current ISO dimensions differ by 1 mm across the flats on three thread sizes.
M10
ISO
16 mm
→
Older DIN
17 mm
M12
ISO
18 mm
→
Older DIN
19 mm
M14
ISO
21 mm
→
Older DIN
22 mm
02
SAE FASTENER LOOKUP
SAE Bolt Diameter to Socket Size
Standard hex-series reference following ASME B18.2.1. Heavy hex fasteners use a head one size larger, and some machine screws use a smaller head than the bolt diameter suggests.
| Bolt Diameter | Socket 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: Read This Before You Apply Torque.
Wrench charts show nominal dimensions. Three variables move a head size away from the printed value: head standard and series, coating thickness, and condition or reuse.
NOMINAL ≠ ACTUAL
A Chart Gives You the Nominal Size
A chart value is nominal. Standards set tolerances on both sides of the joint rather than a single fixed value. None of this makes the tables wrong—it makes them nominal.
CHART VALUE
Nominal
Standard head dimension
→
ACTUAL FASTENER
Measure
Real width across flats
If a fastener is critical, measure it.
If it is coated, measure it and expect to go up a size.
01
Head Standard & Series
STANDARDISO, DIN and ANSI define different head dimensions for the same thread size. Standard hex and heavy hex differ again, often by one socket size.
02
Coating Thickness
FINISHHot-dip galvanizing adds measurable thickness to the head. A galvanized nut can need the next size up where a plain one does not.
Plain
Coated
Heavy Coating
03
Condition & Reuse
CONDITIONA worn, rounded, painted or corroded head is no longer at nominal size, and no chart accounts for it.
PRACTICAL RULE
Use the chart to identify the nominal size.
Use the actual fastener to confirm the fit.
If it is coated, measure it and expect to go up a size. A wrench that rocks under load is not correct simply because its nominal size appears close.
FINAL CHECK
Measure A/F
BUYER RANGE PLANNING
What Wrench Sizes Should Your Range Carry?
Choosing a range is different from matching one fastener. For importers 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
8–22
mm
A working set spans roughly 8 mm to 22 mm, with larger sets running to 32 mm. Demand is not evenly distributed across that range.
10
mm
13
mm
17
mm
19
mm
High-frequency core sizes
These sizes—plus 14 mm on the socket side—carry a disproportionate share of everyday use, wear, loss and reorders in a metric program.
COMMONLY OMITTED
The Sizes Basic Sets Skip
Lower-priced metric sets routinely drop sizes to reduce piece count and hit a target retail price. Two sizes deserve particular attention.
OFTEN SKIPPED
16
mm
+
OFTEN SKIPPED
18
mm
WHY THEY MATTER
These are exactly the sizes made necessary by the DIN-to-ISO head change. Markets with older equipment in service will notice the omission—and trade-channel complaints often start here.
SAE CORE RANGE
Start With the Sizes That Cover General North American Work
A core SAE program concentrates on 1/4″ through 3/4″, with 3/8″ and 7/16″ among the most common. Sizes above 1″ move far more slowly and belong in a supplementary program, not an opening order.
1/4″
Core Start
1/2″
Core
3/4″
Core End
1″+
Supplementary
PRODUCT CONFIGURATION
Size Progression Sets the Price Point
The same forging platform can produce several retail positions through size progression and head configuration. Impact sockets are a separate material, finish and price point—plan and quote them as their own line.
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 final retail price.
Lower Entry Price
03
TOOL CONFIGURATION
6-Point or 12-Point
Head geometry creates another product tier and changes application positioning even when the nominal size spread stays 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. For a specific set, use the hand tool set configurator for piece count and drive mix.
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.
What is the difference between socket size and drive size?
Socket size is the hex opening that grips the fastener, such as 13 mm. Drive size is the square end that connects to the ratchet, such as 3/8″. They are separate measurements. Socket size sets the fit, drive size sets how much torque the tool can transmit, and a socket is always marked with both.
Is a 13 mm socket the same as a 1/2 inch?
No. A 1/2″ head measures 12.70 mm across the flats, so a 13 mm socket 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″ socket measures 12.70 mm and will not fit a 13 mm head.
What size socket do I need for a 10 mm bolt?
It depends on the head, not the thread. If you mean an M10 metric fastener, the 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 socket. If you mean a bolt with a 10 mm head, measure across the flats and use a 10 mm socket.
Are metric and SAE sockets interchangeable?
Only in a few specific pairs and only in one direction. The closest pairs are 27 mm with 1-1/16″, 19 mm with 3/4″, and 8 mm with 5/16″, all within about 0.06 mm. Gaps beyond roughly 0.3 mm to 0.5 mm let the socket walk under load. Never substitute on high-torque, seized, rusted or galvanized fasteners.
How do I measure a nut to find the socket 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 socket seats fully with no side-to-side movement.
What socket sizes should be in a basic set?
A metric set should span 8 mm to 22 mm with 10, 13, 17 and 19 mm as the high-use sizes, and should 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.