SocketFinderUSA

SOCKETFINDERUSA / SHOP REFERENCE

Know the size.
Get the fit right.

Convert metric and SAE sizes, identify a fastener from your measurements, and find tap drills or clearance holes.

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Chrome 16 mm socket, wrench, bolt and nut on a workbench
MEASURE • MATCH • WORK

Convert sizes

Compare a metric or SAE size with the closest common tool size. A close number is not a fit guarantee.

Measure a fastenerIdentify thread, length and head style →Tap drill chartCheck a bit before you drill →Common size chartsBrowse metric and SAE bolt heads →

SHOP REFERENCE / 01

Common fastener sizes

Choose Metric or Standard, then open a size for its thread and tool details.

Thread sizeOutside diameter identifies the fastener.
Thread spacingPitch in mm or threads per inch (TPI) identifies the thread.
Head across flatsThe distance between opposite flat faces identifies the wrench or socket opening.

M3Coarse pitch0.5 mmISO hex tool5.5 mmSocket cap key2.5 mm
Thread outside diameter
3 mm
Common coarse pitch
0.5 mm
Fine pitch options covered
No fine option in this chart; verify the actual thread
Modern ISO hex head tool
5.5 mm
Older DIN hex head tool
Same as ISO (5.5 mm)
Socket cap screw Allen key
2.5 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M3 in Find My Fastener →
M4Coarse pitch0.7 mmISO hex tool7 mmSocket cap key3 mm
Thread outside diameter
4 mm
Common coarse pitch
0.7 mm
Fine pitch options covered
No fine option in this chart; verify the actual thread
Modern ISO hex head tool
7 mm
Older DIN hex head tool
Same as ISO (7 mm)
Socket cap screw Allen key
3 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M4 in Find My Fastener →
M5Coarse pitch0.8 mmISO hex tool8 mmSocket cap key4 mm
Thread outside diameter
5 mm
Common coarse pitch
0.8 mm
Fine pitch options covered
No fine option in this chart; verify the actual thread
Modern ISO hex head tool
8 mm
Older DIN hex head tool
Same as ISO (8 mm)
Socket cap screw Allen key
4 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M5 in Find My Fastener →
M6Coarse pitch1 mmISO hex tool10 mmSocket cap key5 mm
Thread outside diameter
6 mm
Common coarse pitch
1 mm
Fine pitch options covered
0.75 mm
Modern ISO hex head tool
10 mm
Older DIN hex head tool
Same as ISO (10 mm)
Socket cap screw Allen key
5 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M6 in Find My Fastener →
M7Coarse pitch1 mmISO hex tool11 mmSocket cap key—
Thread outside diameter
7 mm
Common coarse pitch
1 mm
Fine pitch options covered
No fine option in this chart; verify the actual thread
Modern ISO hex head tool
11 mm
Older DIN hex head tool
Same as ISO (11 mm)
Socket cap screw Allen key
No value in this reference

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M7 in Find My Fastener →
M8Coarse pitch1.25 mmISO hex tool13 mmSocket cap key6 mm
Thread outside diameter
8 mm
Common coarse pitch
1.25 mm
Fine pitch options covered
1 mm
Modern ISO hex head tool
13 mm
Older DIN hex head tool
Same as ISO (13 mm)
Socket cap screw Allen key
6 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M8 in Find My Fastener →
M10Coarse pitch1.5 mmISO hex tool16 mmSocket cap key8 mm
Thread outside diameter
10 mm
Common coarse pitch
1.5 mm
Fine pitch options covered
1.25 mm, 1 mm
Modern ISO hex head tool
16 mm
Older DIN hex head tool
17 mm
Socket cap screw Allen key
8 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M10 in Find My Fastener →
M12Coarse pitch1.75 mmISO hex tool18 mmSocket cap key10 mm
Thread outside diameter
12 mm
Common coarse pitch
1.75 mm
Fine pitch options covered
1.5 mm, 1.25 mm
Modern ISO hex head tool
18 mm
Older DIN hex head tool
19 mm
Socket cap screw Allen key
10 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M12 in Find My Fastener →
M14Coarse pitch2 mmISO hex tool21 mmSocket cap key12 mm
Thread outside diameter
14 mm
Common coarse pitch
2 mm
Fine pitch options covered
1.5 mm
Modern ISO hex head tool
21 mm
Older DIN hex head tool
22 mm
Socket cap screw Allen key
12 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M14 in Find My Fastener →
M16Coarse pitch2 mmISO hex tool24 mmSocket cap key14 mm
Thread outside diameter
16 mm
Common coarse pitch
2 mm
Fine pitch options covered
1.5 mm
Modern ISO hex head tool
24 mm
Older DIN hex head tool
Same as ISO (24 mm)
Socket cap screw Allen key
14 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M16 in Find My Fastener →
M18Coarse pitch2.5 mmISO hex tool27 mmSocket cap key14 mm
Thread outside diameter
18 mm
Common coarse pitch
2.5 mm
Fine pitch options covered
No fine option in this chart; verify the actual thread
Modern ISO hex head tool
27 mm
Older DIN hex head tool
Same as ISO (27 mm)
Socket cap screw Allen key
14 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M18 in Find My Fastener →
M20Coarse pitch2.5 mmISO hex tool30 mmSocket cap key17 mm
Thread outside diameter
20 mm
Common coarse pitch
2.5 mm
Fine pitch options covered
No fine option in this chart; verify the actual thread
Modern ISO hex head tool
30 mm
Older DIN hex head tool
Same as ISO (30 mm)
Socket cap screw Allen key
17 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M20 in Find My Fastener →
M22Coarse pitch2.5 mmISO hex tool34 mmSocket cap key17 mm
Thread outside diameter
22 mm
Common coarse pitch
2.5 mm
Fine pitch options covered
No fine option in this chart; verify the actual thread
Modern ISO hex head tool
34 mm
Older DIN hex head tool
32 mm
Socket cap screw Allen key
17 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M22 in Find My Fastener →
M24Coarse pitch3 mmISO hex tool36 mmSocket cap key19 mm
Thread outside diameter
24 mm
Common coarse pitch
3 mm
Fine pitch options covered
No fine option in this chart; verify the actual thread
Modern ISO hex head tool
36 mm
Older DIN hex head tool
Same as ISO (36 mm)
Socket cap screw Allen key
19 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M24 in Find My Fastener →
M27Coarse pitch3 mmISO hex tool41 mmSocket cap key19 mm
Thread outside diameter
27 mm
Common coarse pitch
3 mm
Fine pitch options covered
No fine option in this chart; verify the actual thread
Modern ISO hex head tool
41 mm
Older DIN hex head tool
Same as ISO (41 mm)
Socket cap screw Allen key
19 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M27 in Find My Fastener →
M30Coarse pitch3.5 mmISO hex tool46 mmSocket cap key22 mm
Thread outside diameter
30 mm
Common coarse pitch
3.5 mm
Fine pitch options covered
No fine option in this chart; verify the actual thread
Modern ISO hex head tool
46 mm
Older DIN hex head tool
Same as ISO (46 mm)
Socket cap screw Allen key
22 mm

Head style and applicable standard determine the actual tool size. Confirm the thread pitch and measure across the head flats before buying.

Use M30 in Find My Fastener →

These are nominal reference values for common hex bolts and full-height socket cap screws. Fine pitch, older DIN and heavy hex dimensions appear inside the relevant row where covered. A dash means no verified value in this chart. Actual heads, nuts and specialty hardware may differ. See reference sources.

Frequently asked questions

Why does an M10 bolt sometimes use a 16 mm wrench and sometimes a 17 mm wrench?

Modern ISO 4014 / 4017 M10 standard hex bolts use a 16 mm wrench. Older DIN 931 / 933 dimensions use 17 mm, and that hardware is still common. M12 changes from 19 mm DIN to 18 mm ISO; M14 from 22 to 21 mm. M22 goes the other way: 32 mm DIN versus 34 mm ISO. Identify the standard or measure the actual head.

Can I use an SAE socket on a metric bolt?

Use the correct size whenever possible. Some nominal sizes are very close: 3/4 inch equals 19.05 mm, just 0.05 mm from 19 mm. But tolerance, wear and loading affect the fit. A smaller socket may not seat; a larger socket may round the corners. Never force a tool or use one that rocks on the fastener. The conversion labels describe numerical closeness, not a guarantee of interchangeability.

Are bolt diameter and wrench size the same thing?

No. M10 describes a nominal 10 mm thread diameter, not a 10 mm head. A modern ISO M10 standard hex bolt takes a 16 mm wrench; an M10 full-height socket head cap screw takes an 8 mm hex key. The head style matters as much as the thread size.

What does “across flats” mean?

It is the straight-line distance between two opposite flat faces of a hexagonal head or nut. Place the caliper jaws against the flats, not the corners. Clean off dirt first and avoid damaged edges. This distance corresponds to the nominal wrench or socket opening.

Do Allen keys use the same sizing system as normal sockets?

Both come in metric millimeters and SAE inches, but they engage different surfaces. An Allen key fits an internal hexagonal recess; a normal socket fits around the outside of a head. An M8 ISO hex bolt uses a 13 mm socket, while an M8 full-height socket head cap screw uses a 6 mm hex key. Button, flat and low-profile heads need their own charts. Use the exact key size.

How do I measure a bolt if I don’t know its size?

Use calipers to measure across the head flats for an initial tool choice. To identify the bolt itself, measure the outside diameter of the threads and use a thread-pitch gauge to find metric pitch or inch threads per inch. Measure length from under the head to the tip for a standard hex or socket cap screw. Compare the head style and measurements with a verified reference; a wrench size alone cannot identify the thread.

How do I tell metric pitch from SAE TPI?

Metric pitch is the distance between adjacent thread peaks in millimeters. TPI counts thread peaks per inch. Measure across several gaps or use a thread gauge; confirm before ordering a replacement.

Is a tap drill the same as a clearance hole?

No. A tap drill makes the pilot hole for cutting internal threads. A clearance hole is larger than the bolt thread so the bolt passes through freely. Check your tap type, material and fit requirement before drilling.

SHOP REFERENCE / 02

Measure a fastener in four steps

Use a caliper and a thread gauge if you have them. Write down each measurement before searching for a replacement.

  1. Thread diameterMeasure straight across the outside of the threads, over the highest points. This is the bolt’s nominal size: about 8 mm suggests M8; about 1/4″ suggests a 1/4″ thread.
  2. Pitch or threads per inchMetric pitch is the gap from one thread peak to the next in millimeters. For SAE, count the threads in one inch. A gauge is best; the same diameter can have coarse or fine threads.
  3. LengthFor a standard hex or socket cap bolt, measure from under the head to the tip. For a countersunk flat head, measure the full length including the head.
  4. Head across flatsOn a hex head or nut, measure between two opposite flat faces, not corner to corner. This determines the socket or wrench opening, not the thread diameter.
Head flatsLength under headThread ØPitch

Example: M8 × 1.25 × 30 mm means 8 mm thread diameter, 1.25 mm between thread peaks, and 30 mm length. The head style and actual head measurement still matter.

SHOP REFERENCE / 03

Put sockets and wrenches back in order

Read left to right, smallest to largest. Use the same order for a socket rail or an open-end wrench rack. Keep metric and SAE in separate rows.

Metric millimeters

  1. 4 mm
  2. 4.5 mm
  3. 5 mm
  4. 5.5 mm
  5. 6 mm
  6. 7 mm
  7. 8 mm
  8. 9 mm
  9. 10 mm
  10. 11 mm
  11. 12 mm
  12. 13 mm
  13. 14 mm
  14. 15 mm
  15. 16 mm
  16. 17 mm
  17. 18 mm
  18. 19 mm
  19. 20 mm
  20. 21 mm
  21. 22 mm
  22. 23 mm
  23. 24 mm
  24. 25 mm
  25. 26 mm
  26. 27 mm
  27. 28 mm
  28. 29 mm
  29. 30 mm
  30. 32 mm

SAE inches

  1. 1/4″
  2. 5/16″
  3. 3/8″
  4. 7/16″
  5. 1/2″
  6. 9/16″
  7. 5/8″
  8. 11/16″
  9. 3/4″
  10. 13/16″
  11. 7/8″
  12. 15/16″
  13. 1″
  14. 1-1/16″
  15. 1-1/8″
  16. 1-3/16″
  17. 1-1/4″
  18. 1-5/16″
  19. 1-3/8″
  20. 1-7/16″
  21. 1-1/2″

This covers a useful range of commonly encountered hand-tool sizes. Your set may skip sizes or include smaller or larger ones. Put any extra size in numerical order between its neighbors; do not mix an SAE tool into a metric row just because it looks close.

About SocketFinder & sources

A practical fastener and shop reference. All calculations run in your browser, with no accounts or external API. Dimensions are nominal tool sizes; the cited references define the applicable fastener styles.

ISO / DIN hex dimensions · StainlessFixM7 hex dimensions · McMaster-CarrISO 4762 socket caps · RC Fasteners (PDF)Metric DIN 912 hex keys · AIMS IndustrialUS hex & heavy hex · Bolt DepotASME B18.3 hex keys · TorqBoltDIN 934 nuts · Tank FastenersUS hex nuts · Bolt DepotM7 nut · HoenderdaalTap drills · LittleMachineShopClearance holes · Albany County Fasteners (PDF)

Reference tables checked September 25, 2026. Thread identification and drill charts cover the common sizes listed here. Specialty fasteners may differ. Standard hex nuts are included separately: DIN 934 metric and US hex nuts. Other nut styles can differ.

Fastener dimensions can vary by standard, manufacturer, age, and head style. SocketFinder is a reference tool; confirm the fastener before applying high torque.