Hex Bolt
Bolts · hex head cap screw · hex cap screw · machine bolt
Anatomy
Governing standards: ASME B18.2.1 · SAE J429 · ISO 4014 · DIN 933
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| 1/4-20 | M6 x 1.0 | 7/16 | 5/32 |
| 3/8-16 | M10 x 1.5 | 9/16 | 15/64 |
| 1/2-13 | M12 x 1.75 | 3/4 | 5/16 |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| Grade 2 | low/medium carbon steel | 74,000 | No head marking |
| Grade 5 | medium carbon steel, quenched & tempered | 120,000 | 3 radial lines |
| Grade 8 | medium carbon alloy steel, quenched & tempered | 150,000 | 6 radial lines |
Torque Reference (in-lb)
| Diameter | Grade 2 | Grade 5 | Grade 8 |
|---|---|---|---|
| 1/4-20 | 75 | 120 | 170 |
| 3/8-16 | 270 | 430 | 610 |
| 1/2-13 | 640 | 1020 | 1440 |
Dry, non-lubricated assembly values. Lubricated threads can require 20–30% less torque. Verify against your standard.
Materials
- Zinc-plated steel
- Stainless steel (304 / 316)
- Brass
- Silicon bronze
- Hot-dip galvanized steel
Pros & Cons
Pros
- Very high strength, especially Grade 8
- Widely available in any hardware store
- Removable and reusable
Cons
- Requires a wrench or socket (access to the head and nut)
- Heavier than a comparable screw
- Corrodes unless coated or stainless
Typical Uses
- Machinery assembly
- Construction and structural steelwork
- Automotive repair
- General manufacturing
Alternatives & Related
- Carriage Bolt — Domed head for wood; no wrench needed on the head side
- Socket Head Cap Screw — Higher strength per size, compact cylindrical head
- Lag Bolt — Threads directly into wood without a nut
Top Picks
- Grade 5 hex bolt assortment — Zinc-plated, 100+ pcs
- Stainless hex bolt kit — 304 stainless, SAE + metric
Where to Buy
Affiliate links — we may earn a commission at no cost to you.
FAQ
What is the difference between a hex bolt and a hex cap screw?
In common use the terms overlap. Strictly, a hex cap screw has a washer face under the head and tighter dimensional tolerances (ASME B18.2.1), while a hex bolt has a plain bearing face. For most buying decisions they are interchangeable.
What grade hex bolt should I use?
Grade 2 for light general use; Grade 5 for most automotive and machinery work; Grade 8 for high-stress, high-clamp applications. Match the grade to the load — a Grade 8 bolt will not compensate for a poor joint design.
Are hex bolts reusable?
Yes, if undamaged and not stretched past yield. Replace any bolt with deformed threads, necking, or corrosion pitting.