What size wrench or spanner fits 3/8 in?

3/8 in bolt uses a 9/16 wrench or spanner, measured across the flats of the hex head.

What is the torque for 3/8 in?

A typical tightening torque for 3/8 in bolt in Grade 5 on dry threads is about 47 Nm (34.7 ft·lb). Always confirm against the manufacturer spec for important joints.

What thread pitch and tap drill does 3/8 in use?

3/8 in bolt has a thread pitch of 16 TPI (threads per inch) and uses a 5/16 (7.9 mm) tap drill, with a 25/64 clearance hole.

What is 3/8 in used for?

3/8 in is commonly used in automotive, heavy machinery, structural. It is one of the most popular sizes in its category.

What is the closest metric size to 3/8 in?

The closest metric size to 3/8 in is approximately ~M10, though they are not exactly interchangeable.

Home › Imperial / SAE Bolts › 3/8 in

3/8 in bolt size

9/16 wrench

across-flats spanner / socket size for 3/8 in

3/8 in bolt — Automotive, heavy machinery, structural.

Full specification

System	Imperial UNC
Nominal diameter	3/8 in (0.375 in / 9.53 mm)
Thread pitch	16 TPI
Wrench / spanner (across flats)	9/16
Tap drill	5/16 (7.9 mm)
Clearance hole	25/64
Common grade / class	Grade 5
Typical torque	47 Nm (34.7 ft·lb)
Closest other-system size	~M10

🔧 Torque unit converter

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

Pre-filled with the typical torque for 3/8 in (Grade 5, dry). Edit any field to convert.

⚠️ Torque values here are general references for Grade 5 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 3/8 in

Automotive, heavy machinery, structural.

A 5/16 drill is the standard tap drill for 3/8 in-16 UNC thread. The standard clearance hole is 25/64.

3/8 in is part of the Unified National Coarse (UNC) thread series, defined in ASME B1.1. The wrench size 9/16 is measured across the flats of the hex head.

Common applications

3/8 in bolts are widely used in:

Automotive, heavy machinery, structural
General machinery and equipment assembly
Automotive components and repairs
Structural connections (when specified by engineer)
Industrial maintenance and repair

Material and grade information

The typical grade for 3/8 in is Grade 5. This indicates:

Grade 5: Medium carbon steel, quenched and tempered
Tensile strength: 120,000 PSI
Yield strength: 92,000 PSI
Common coatings: Zinc plated, hot-dip galvanized, or plain

Frequently asked questions

What size wrench or spanner fits 3/8 in?: 3/8 in bolt uses a 9/16 wrench or spanner, measured across the flats of the hex head.
What is the torque for 3/8 in?: A typical tightening torque for 3/8 in bolt in Grade 5 on dry threads is about 47 Nm (34.7 ft·lb). Always confirm against the manufacturer spec for important joints.
What thread pitch and tap drill does 3/8 in use?: 3/8 in bolt has a thread pitch of 16 TPI (threads per inch) and uses a 5/16 (7.9 mm) tap drill, with a 25/64 clearance hole.
What is 3/8 in used for?: 3/8 in is commonly used in automotive, heavy machinery, structural. It is one of the most popular sizes in its category.
What is the closest metric size to 3/8 in?: The closest metric size to 3/8 in is approximately ~M10, though they are not exactly interchangeable.