Top M4 Stainless Steel Hex Bolts for Rust-Free Fastening
For most users, the overall best is the Hilitchi 210-Piece M4 Stainless Steel Hex Bolt Assortment. It offers a comprehensive range of lengths, 304 stainless steel for good corrosion resistance, and a durable storage case. Its main limitation is that 304 steel is not ideal for marine or highly corrosive environments. If you need maximum strength and corrosion resistance for demanding applications, consider the M4-0.7 x 16mm Button Head Hex Socket Cap Screws by Bolts Unlimited, which use 316 stainless steel.
Stainless steel hex bolts are essential for projects that demand corrosion resistance and a clean appearance. M4 bolts are common in electronics, small machinery, and hobbyist builds. Choosing the right grade and length ensures a secure, long-lasting fastening.
The market offers many M4 stainless steel hex bolts, but not all are created equal. We compared top-selling sets based on material quality, variety, and user satisfaction. Our picks range from budget-friendly assortments to premium 316 stainless steel options.
Before you buy
What we recommend
Hilitchi 210-Piece M4 Stainless Steel Hex Bolt Assortment
This comprehensive set includes M4 hex bolts in 13 different lengths, from 6mm to 40mm. Made from 304 stainless steel, it offers good corrosion resistance for indoor and outdoor use. The bolts come in a sturdy clear storage box, making organization easy. Users praise the quality and the convenience of having multiple sizes on hand.
Pros
- Great variety of lengths for different projects
- Good corrosion resistance for most applications
- Clear case keeps bolts organized and accessible
Cons
- Not suitable for marine environments
- Some users report occasional burrs on threads
Bolts Unlimited M4-0.7 x 16mm Button Head Hex Socket Cap Screws
These button head hex socket cap screws are made from 316 stainless steel, which offers superior resistance to chlorides and chemicals compared to 304. This makes them ideal for marine, coastal, and chemical environments. The low-profile button head provides a clean finish, and the hex socket drive allows for secure fastening with an Allen key.
Pros
- Premium 316 stainless steel for harsh environments
- Low-profile head fits flush in many applications
- High user satisfaction with quality and finish
Cons
- Only one length available per pack
- Higher cost than 304 stainless steel
Lehigh 500-Piece M4 Stainless Steel Hex Bolt Assortment
Lehigh offers a massive 500-piece assortment of M4 hex bolts, covering lengths from 5mm to 40mm. Made from 304 stainless steel, these bolts are suitable for many DIY and professional uses. The set comes with a durable storage case with clear dividers. This is a cost-effective solution for anyone who frequently needs M4 bolts.
Pros
- Exceptional value with 500 pieces
- Wide range of lengths covers most needs
- Sturdy case keeps bolts sorted
Cons
- May be more than a casual user needs
- Some lengths may have limited quantities
Shenzhen Yiyi M4 x 10mm Stainless Steel Hex Bolts (50-Pack)
If you need a specific size, this 50-pack of M4 x 10mm hex bolts is a solid choice. Made from 304 stainless steel, they offer dependable performance. The hex head allows for easy tightening with a wrench or socket. Users appreciate the consistent threading and smooth finish.
Pros
- Exactly the size you need without extras
- Good quality for the price
- Strong threading and clean finish
Cons
- Limited to a single length
- No storage case included
DYWISHKEY M4 x 6mm Stainless Steel Hex Socket Cap Screws (100-Pack)
These short M4 x 6mm hex socket cap screws are perfect for tight spaces where a standard hex head bolt won’t fit. The socket cap design allows for easy installation with a hex key. Made from 304 stainless steel, they provide good corrosion resistance. This 100-pack is ideal for electronics and small repairs.
Pros
- Very short length for confined spaces
- Socket cap allows for secure tightening
- High count at an affordable price
Cons
- Not suitable for applications requiring deep threading
- Only one size available
Bolts and Nuts M4 x 20mm Hex Bolts with Nuts and Washers (50 Sets)
This kit includes 50 M4 x 20mm hex bolts, along with matching nuts and washers, all made from 304 stainless steel. It provides everything you need to secure components. The bolts are fully threaded, offering flexibility for various thicknesses. Users find it convenient to have the matching hardware in one package.
Pros
- Complete kit with nuts and washers
- Fully threaded for versatile use
- Good corrosion resistance
Cons
- Only one length and size available
- Nuts may be thin for some users
Muzata M4 x 30mm Hex Bolts, 25-Pack, 304 Stainless Steel
These M4 x 30mm hex bolts are designed for applications requiring a longer shank. Made from 304 stainless steel, they offer solid strength and corrosion resistance. The hex head provides a good grip for wrenches. This 25-pack is suitable for assembling frames or securing thicker materials.
Pros
- Longer length for thicker materials
- Reliable 304 stainless steel
- Good value for the number of bolts
Cons
- Fewer pieces per pack compared to others
- No washers or nuts included
The lineup, side by side
| # | Model | Material | Best for | Score | Price |
|---|---|---|---|---|---|
| 1 | Hilitchi 210-Piece M4 Stainless Steel Hex Bolt Assortment | 304 stainless steel | Best overall for variety and value | 9.4 | Check price |
| 2 | Bolts Unlimited M4-0.7 x 16mm Button Head Hex Socket Cap Screws | 316 stainless steel | Best for maximum corrosion resistance with 316 stainless steel | 9.2 | Check price |
| 3 | Lehigh 500-Piece M4 Stainless Steel Hex Bolt Assortment | 304 stainless steel | Best for bulk quantity and variety | 9.0 | Check price |
| 4 | Shenzhen Yiyi M4 x 10mm Stainless Steel Hex Bolts (50-Pack) | 304 stainless steel | Best for small projects needing a single length | 8.8 | Check price |
| 5 | DYWISHKEY M4 x 6mm Stainless Steel Hex Socket Cap Screws (100-Pack) | 304 stainless steel | Best for low-profile applications | 8.6 | Check price |
| 6 | Bolts and Nuts M4 x 20mm Hex Bolts with Nuts and Washers (50 Sets) | 304 stainless steel | Best complete fastening kit | 8.5 | Check price |
| 7 | Muzata M4 x 30mm Hex Bolts, 25-Pack, 304 Stainless Steel | 304 stainless steel | Best for longer reach applications | 8.3 | Check price |
Common questions
What does M4 mean on a hex bolt?
M4 refers to the metric thread size: the nominal outer diameter of the thread is 4 millimeters. The standard thread pitch for M4 is 0.7mm, meaning the distance between threads is 0.7mm. This is the most common pitch for M4 bolts, but finer pitches exist, so always confirm.
What is the difference between 304 and 316 stainless steel?
Both are austenitic stainless steels, but 316 contains molybdenum, which enhances its resistance to chlorides (like saltwater) and acids. 316 is more expensive and is recommended for marine or highly corrosive environments. 304 is suitable for most general applications that require corrosion resistance.
How do I measure the length of a hex bolt?
For most bolts, the length is measured from the underside of the head to the end of the threaded portion. For hex bolts with a flat head, measure from the top of the head. Always measure in millimeters for metric bolts. For example, an M4 x 20mm bolt is 20mm long from under the head to the tip.
Can M4 stainless steel hex bolts be used outdoors?
Yes, 304 stainless steel is suitable for outdoor use in most climates. It resists rust and corrosion from moisture. However, in coastal areas with high salt exposure, 316 stainless steel is a better choice. Always check the grade before installing in harsh environments.
What tools do I need to install M4 hex bolts?
To install a standard hex bolt, you need a wrench, socket, or pliers that fit the head size. For M4 bolts, the head is typically 7mm across flats, so a 7mm wrench or socket is common. For socket head cap screws, you need the appropriate hex key (Allen wrench), usually 3mm for M4.
Are M4 stainless steel hex bolts magnetic?
Austenitic stainless steels like 304 and 316 are generally non-magnetic in the annealed state. However, cold working during manufacturing can make them slightly magnetic. This is normal and does not affect corrosion resistance.
How much weight can an M4 bolt hold?
The strength of an M4 bolt depends on its material and grade. Stainless steel bolts like 304 have a tensile strength of about 620 MPa. The shear strength is typically about 60% of tensile. For a single M4 bolt, the safe working load is around 200-300 kg in shear, but always consult engineering standards for structural applications.
Can I reuse M4 stainless steel hex bolts?
Yes, stainless steel bolts can be reused as long as they are not damaged. However, repeated tightening may cause galling, where the threads bind together. Applying an anti-seize lubricant can help prevent this. Inspect bolts for thread damage or stretching before reusing in critical applications.
Our take
For most DIY and professional needs, the Hilitchi 210-Piece Assortment is the best buy because it offers a wide range of sizes and reliable 304 stainless steel at a reasonable cost. If your project involves harsh or marine environments, upgrade to the Bolts Unlimited 316 stainless steel set, despite the higher price and limited length options. Avoid sacrificing quality for sheer quantity; the Lehigh 500-Piece set is a close second, but the Hilitchi case and reputation make it the top pick.
Jake Monroe
Jake worked as a residential contractor for over a decade before shifting to full-time writing. He evaluates power tools, hand tools and workshop gear through the lens of someone who has actually used them on job sites, not just read the box.
