What size wrench or spanner fits M8?

M8 bolt uses a 13 mm wrench or spanner, measured across the flats of the hex head.

What is the torque for M8?

A typical tightening torque for M8 bolt in 8.8 on dry threads is about 25 Nm (18.4 ft·lb). Always confirm against the manufacturer spec for important joints.

What thread pitch and tap drill does M8 use?

M8 bolt has a thread pitch of 1.25 mm and uses a 6.8 mm tap drill, with a 9 mm clearance hole.

M8 is commonly used in automotive, machinery, furniture, structural. It is one of the most popular sizes in its category.

What is the closest imperial size to M8?

The closest imperial size to M8 is approximately ~5/16 inch, though they are not exactly interchangeable.

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M8 bolt size

13 mm wrench

across-flats spanner / socket size for M8

M8 bolt — Automotive, machinery, furniture, structural.

Full specification

System	Metric coarse
Nominal diameter	8 mm
Thread pitch	1.25 mm
Wrench / spanner (across flats)	13 mm
Tap drill	6.8 mm
Clearance hole	9 mm
Common grade / class	8.8
Typical torque	25 Nm (18.4 ft·lb)
Closest other-system size	~5/16 inch

🔧 Torque unit converter

Newton-metres (Nm) Foot-pounds (ft·lb) Inch-pounds (in·lb)

Pre-filled with the typical torque for M8 (8.8, dry). Edit any field to convert.

⚠️ Torque values here are general references for 8.8 on clean, dry threads. Lubrication, coatings, and the joint material change the figure significantly. For structural, automotive, or safety-critical work, always use the torque specified by the manufacturer or engineer.

About M8

Automotive, machinery, furniture, structural.

A 6.8 mm tap drill is correct for M8 coarse thread. The standard clearance hole is 9 mm.

M8 is part of the ISO metric coarse thread series, defined in ISO 261. The wrench size 13 mm is measured across the flats of the hex head.

Common applications

M8 bolts are widely used in:

Automotive, machinery, furniture, structural
General machinery and equipment assembly
Automotive components and repairs
Structural connections (when specified by engineer)
Furniture and fixture assembly

Material and grade information

The typical grade for M8 is 8.8. This indicates:

Property class 8.8: Medium carbon steel, quenched and tempered
Tensile strength: 800 MPa minimum
Yield strength: 640 MPa minimum (0.2% proof stress)
Common coatings: Zinc plated, hot-dip galvanized, or plain

Frequently asked questions

What size wrench or spanner fits M8?: M8 bolt uses a 13 mm wrench or spanner, measured across the flats of the hex head.
What is the torque for M8?: A typical tightening torque for M8 bolt in 8.8 on dry threads is about 25 Nm (18.4 ft·lb). Always confirm against the manufacturer spec for important joints.
What thread pitch and tap drill does M8 use?: M8 bolt has a thread pitch of 1.25 mm and uses a 6.8 mm tap drill, with a 9 mm clearance hole.
What is M8 used for?: M8 is commonly used in automotive, machinery, furniture, structural. It is one of the most popular sizes in its category.
What is the closest imperial size to M8?: The closest imperial size to M8 is approximately ~5/16 inch, though they are not exactly interchangeable.