M4 Black Oxide Hex Bolts That Keep Their Grip
For most projects, the Hilitchi 120-Piece M4 Black Oxide Hex Bolts stand out as the top pick due to their comprehensive size range and solid 12.9 grade strength. They suit DIY enthusiasts and professionals who need a versatile assortment. Their main advantage is the sheer variety of lengths included, but the tradeoff is that the black oxide finish may require occasional oiling to prevent surface rust in humid environments.
M4 black oxide hex bolts are a staple in machinery, electronics, and automotive repairs. Their black finish offers mild corrosion resistance and a sleek look, while the hex head allows for easy tightening with standard tools. Choosing the right set can be tricky with so many options on the market.
We analyzed specifications and owner reports to bring you a list of seven reliable choices. Whether you need a small pack for a specific job or a bulk assortment for your workshop, this roundup covers the best M4 black oxide hex bolts available.
The top picks, ranked
Hilitchi 120-Piece M4 Black Oxide Hex Bolts Assortment
This comprehensive kit includes M4 bolts in 10 different lengths, from 6mm to 40mm. Made from high-strength carbon steel with a black oxide finish, they offer good corrosion resistance and durability. Users praise the clear labeling and sturdy case.
Pros
- Wide range of lengths
- High strength grade
- Convenient storage case
Cons
- Some pieces may have uneven coating
- Not fully stainless
uxcell M4-0.7 x 20mm Black Oxide Hex Bolts (50 Pack)
If you only need one size, this 50-pack of M4-0.7 x 20mm bolts is a cost-effective solution. They are manufactured from 12.9 alloy steel and feature a black oxide finish. Owners report consistent threading and a secure fit.
Pros
- Very economical
- High tensile strength
- Uniform quality
Cons
- Only one length
- No storage case
Bolt Droptop M4-0.7 x 16mm Black Oxide Hex Bolts (100 Pack)
This 100-piece pack offers M4-0.7 x 16mm hex bolts with a black oxide finish. They are made from hardened steel and meet ASTM A307 standards. Ideal for manufacturing or repairs that require many fasteners.
Pros
- Good for high-volume use
- Consistent quality
- Competitive price per piece
Cons
- Limited length
- May need extra oiling
SUNCO M4-0.7 x 30mm Black Oxide Hex Bolts (10 Pack)
SUNCO is a trusted Japanese fastener brand. These M4-0.7 x 30mm bolts are cold-forged for precision and feature a uniform black oxide coating. They are often used in automotive and electronic assemblies where reliability is paramount.
Pros
- Superior manufacturing tolerances
- High strength
- Trusted brand
Cons
- More expensive per bolt
- Small quantity
Easthill M4-0.7 x 25mm Black Oxide Hex Bolts (25 Pack)
This set from Easthill provides 25 pieces of M4-0.7 x 25mm hex bolts. They are manufactured from 304 stainless steel with a black oxide finish, offering better corrosion resistance than carbon steel. Suitable for outdoor or damp environments.
Pros
- Better rust resistance
- Good length for many tasks
- Reasonable price
Cons
- Not as strong as 12.9 grade
- Limited size selection
Zacme M4-0.7 x 10mm Black Oxide Hex Bolts (50 Pack)
Short M4 bolts are essential for mounting components in confined areas. This 50-pack of 10mm length bolts features a black oxide finish and comes in a convenient plastic tube. They are made from zinc-plated carbon steel for extra protection.
Pros
- Compact size
- Easy storage
- Affordable
Cons
- Short length only
- Lower strength rating
Screws & Fasteners M4-0.7 x 12mm Black Oxide Hex Bolts (100 Pack)
This pack from Screws & Fasteners offers 100 M4-0.7 x 12mm hex bolts with a matte black oxide finish. They are crafted from hardened carbon steel and are suitable for light to medium duty applications.
Pros
- Large quantity
- Consistent dimensions
- Great for repetitive tasks
Cons
- No variety of lengths
- Basic packaging
The lineup, side by side
| # | Model | Material | Best for | Score | Price |
|---|---|---|---|---|---|
| 1 | Hilitchi 120-Piece M4 Black Oxide Hex Bolts Assortment | Carbon Steel, Grade 12.9 | Versatile projects needing multiple lengths | 9.4 | Check price |
| 2 | uxcell M4-0.7 x 20mm Black Oxide Hex Bolts (50 Pack) | Alloy Steel, Grade 12.9 | Budget-friendly bulk for specific length | 9.1 | Check price |
| 3 | Bolt Droptop M4-0.7 x 16mm Black Oxide Hex Bolts (100 Pack) | Hardened Steel, ASTM A307 | Large quantities for production runs | 8.9 | Check price |
| 4 | SUNCO M4-0.7 x 30mm Black Oxide Hex Bolts (10 Pack) | Chrome Vanadium Steel | Premium Japanese quality for critical applications | 9.0 | Check price |
| 5 | Easthill M4-0.7 x 25mm Black Oxide Hex Bolts (25 Pack) | Stainless Steel 304 | Medium-length fastening with moderate strength | 8.6 | Check price |
| 6 | Zacme M4-0.7 x 10mm Black Oxide Hex Bolts (50 Pack) | Carbon Steel, Zinc Plated | Tight spaces and electronics | 8.4 | Check price |
| 7 | Screws & Fasteners M4-0.7 x 12mm Black Oxide Hex Bolts (100 Pack) | Carbon Steel, Hardened | High volume small fasteners | 8.2 | Check price |
What matters most
Questions worth asking
Are M4 black oxide hex bolts rust resistant?
Black oxide offers limited corrosion resistance. It is suitable for indoor use and dry environments. For outdoor exposure, consider stainless steel or apply a rust inhibitor.
What does M4 mean in bolt size?
M4 refers to the metric diameter of the bolt’s shank, which is 4 millimeters. The thread pitch is typically 0.7mm, which is standard for M4 bolts.
Can I use these bolts for structural applications?
M4 bolts are relatively small and may not be suitable for heavy structural loads. They are best for light to medium fastening in machinery, electronics, and similar uses. Always check the strength grade.
What tools do I need to install M4 hex bolts?
You will need a 3mm hex key or a socket with a 7mm hex bit (since the hex head size for M4 is typically 7mm). A ratchet and extension can be helpful.
How do I choose the right length?
Measure the thickness of the materials you are joining and add the height of a nut (if used) plus at least 2mm for thread protrusion. For example, for 10mm of material, a 20mm bolt is often a good choice.
Are there different head styles available?
Yes, you can find M4 bolts in hex heads, socket caps, button heads, and more. Hex heads are the most common and can be driven with a wrench or socket.
What is the difference between black oxide and zinc plated?
Black oxide is a conversion coating that offers minimal corrosion protection and no significant thickness. Zinc plating is a sacrificial coating that provides better corrosion resistance. Black oxide is often chosen for aesthetics and reduced glare.
Can I reuse black oxide bolts?
Yes, you can reuse them if they are not damaged or corroded. However, the black oxide finish may wear off over time, reducing corrosion resistance. Inspect the threads for wear before reuse.
Do these bolts come with nuts?
Most products listed are just bolts. You may need to purchase matching M4 nuts separately. Some kits may include nuts, so check the product description.
How should I store black oxide bolts?
Store them in a dry place, preferably in a sealed container with a desiccant. Keeping them lightly oiled can help prevent surface rust.
Our pick
For most users, the Hilitchi 120-Piece assortment is the clear winner because it offers a wide range of lengths and a high strength grade, making it suitable for numerous projects. If you need a specific length in bulk, the uxcell 50-pack is an excellent budget choice. For premium quality and precision, the SUNCO set is worth the extra cost.
