You are manufacturing bolts, screws, or nuts. The fastener will be used outdoors or in a corrosive environment. You need stainless steel bar that machines well, has good strength, and resists rust.

The most common stainless steel grades¹ for fastener manufacturing are 304 (general purpose), 316 (marine grade), 410 (heat treatable for higher strength), and 303 (free-machining for automatic screw machines). ASTM F593² is the standard specification for stainless steel bolts, hex cap screws, and studs.

I have supplied stainless steel bars to fastener manufacturers for many years. A bolt maker used 303 bar for high-volume machine screws. A marine fastener supplier used 316 bar for corrosion-resistant bolts. Let me walk you through the grades and standards for fastener manufacturing.

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What type of stainless steel is used for bolts?

The most common stainless steel grades¹ used for bolts are 304, 316, 410, and 303. Each grade has different properties and applications.

304 is the standard grade for general-purpose bolts (indoor, mild environments). 316 is used for marine and coastal bolts (high corrosion resistance²). 410 is used for high-strength bolts³ (heat treatable). 303 is used for high-volume machined bolts (free-machining⁴).

Fastener Grade Comparison

Let me compare the stainless steel grades¹ used for fasteners.

304 Stainless Steel

Property	Value
Type	Austenitic
Corrosion resistance	Excellent (general)
Strength (annealed)	205 MPa yield
Machinability	Good
Best for	General-purpose bolts, indoor

316 Stainless Steel

Property	Value
Type	Austenitic
Corrosion resistance	Excellent (marine)
Strength (annealed)	205 MPa yield
Machinability	Good (slightly lower than 304)
Best for	Marine, coastal, chemical

410 Stainless Steel

Property	Value
Type	Martensitic
Corrosion resistance	Good
Strength (heat treated)	550-1,000 MPa yield
Machinability	Good (annealed)
Best for	High-strength bolts, wear-resistant

303 Stainless Steel

Property	Value
Type	Austenitic (free-machining4)
Corrosion resistance	Good (slightly lower than 304)
Strength (annealed)	205 MPa yield
Machinability	Excellent
Best for	High-volume automatic screw machine parts

Fastener Selection Guide

Application	Recommended Grade
General indoor bolts	304
Outdoor bolts (inland)	304
Marine / coastal bolts	316
High-strength bolts	410 (heat treated)
High-volume machine screws	303
Chemical plant bolts	316

My Experience
For a marine hardware manufacturer, we supply 316 bar for bolts exposed to saltwater. For a general hardware supplier, we supply 304 bar.

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Which is better, 304 or 316 stainless steel bolts¹?

316 stainless steel bolts¹ are better for marine, coastal, and high-chloride environments. 304 stainless steel bolts² are better for general use and cost less.

304 bolts are sufficient for most indoor and inland outdoor applications. They resist rust well and cost 20-30% less than 316. 316 bolts contain molybdenum, which provides superior resistance to salt, chlorides, and pitting. For coastal construction, boat hardware, or chemical plants, 316 is the better choice.

304 vs 316 Bolt Comparison

Let me compare 304 and 316 bolts in detail.

304 Bolts

Property	Value
Corrosion resistance	Excellent for general use
Salt resistance	Moderate
Strength	205 MPa yield (property class 70)
Cost	Lower
Best for	Indoor, general outdoor (inland)
Common applications	Furniture, appliances, general construction

316 Bolts

Property	Value
Corrosion resistance	Excellent for marine
Salt resistance	High
Strength	205 MPa yield (property class 70)
Cost	Higher (20-30%)
Best for	Marine, coastal, chemical
Common applications	Boat hardware, coastal construction, pool equipment

Corrosion Comparison

Environment	304 Bolt	316 Bolt
Indoor, dry	Excellent	Excellent
Outdoor, inland	Good	Excellent
Coastal (salt air)	Fair (may rust)	Excellent
Seawater immersion	Poor (pitting)	Good
Deicing salts	Fair	Excellent

Property Classes for Stainless Bolts

Grade	Property Class	Yield Strength (MPa)
304 (annealed)	70	210
304 (cold worked)	80	480
316 (annealed)	70	210
316 (cold worked)	80	480

My Experience
For a beachfront deck, we specified 316 bolts. For an inland warehouse, we specified 304 bolts to save cost.

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How are stainless steel bars made?

Stainless steel bars are made through a process of melting, casting, hot rolling¹, and cold finishing². The raw material is melted in an electric arc furnace³, refined in an AOD vessel, cast into billets, hot rolled into bar, and then cold finished (cold drawing or grinding) to achieve precise dimensions and surface finish.

For fastener manufacturing, cold drawn bar⁴ is preferred because it has tight tolerances, good surface finish, and improved mechanical properties from work hardening.

Bar Manufacturing Process

Let me walk you through the bar manufacturing process.

Step 1: Melting and Refining

• Scrap and alloys melted in electric arc furnace³
• Refined in AOD (Argon Oxygen Decarburization)
• Chemistry adjusted to grade specification

Step 2: Continuous Casting

• Molten steel cast into billets (round or square)
• Billet size: 130-200mm square or round
• Billets are cut to length

Step 3: Hot Rolling

• Billets reheated to 1,200°C
• Rolled through roughing and finishing stands
• Hot rolled bar produced (round, hex, square)

Step 4: Annealing and Pickling

• Hot rolled bar is annealed (softened)
• Pickled to remove scale
• Result: Hot rolled, annealed, pickled bar

Step 5: Cold Finishing (Optional)

• Cold drawing: Pulled through die for precise size
• Centerless grinding: Ground to tight tolerance (h9, f7)
• Polishing: Improved surface finish

Cold Finished Bar Benefits for Fasteners

Benefit	Description
Tight tolerance	±0.025-0.05mm
Good surface finish	No scale, smooth
Improved strength	Work hardened
Straightness	Better than hot rolled

Bar Forms for Fastener Manufacturing

Form	Typical Use
Round bar	Bolts, screws, studs
Hex bar	Hex bolts, nuts
Square bar	Carriage bolts

My Experience
For a bolt manufacturer, we supply cold drawn 303 round bar with h9 tolerance. The bar feeds directly into their automatic screw machines.

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What is the ASTM standard for stainless steel fasteners¹?

The main ASTM standard for stainless steel fasteners¹ is ASTM F593² (for bolts, hex cap screws, and studs). Other important standards include ASTM F594 (nuts), ASTM F738 (metric bolts), and ASTM A193 (high-temperature bolts).

ASTM F593² covers stainless steel bolts in grades 304, 316, 410, and others. It specifies mechanical properties (property class 70 or 80), chemical composition, and testing requirements. Fasteners are marked with the manufacturer's identifier and the material grade.

ASTM Fastener Standards

Let me list the key ASTM standards for stainless steel fasteners¹.

Primary Standards

Standard	Title	Covers
ASTM F5932	Stainless Steel Bolts, Hex Cap Screws, and Studs	Bolts, screws, studs
ASTM F594	Stainless Steel Nuts	Nuts
ASTM F738	Metric Stainless Steel Bolts	Metric bolts
ASTM A193	Alloy and Stainless Steel Bolting for High Temperature	High-temperature service

ASTM F593² Alloy Groups

Group	Grades	Property Class
1	304, 305, 384	70 (annealed), 80 (cold worked)
2	316	70 (annealed), 80 (cold worked)
3	410	70 (heat treated)
4	430	70 (annealed)

Mechanical Requirements (ASTM F593²)

Property Class	Diameter	Yield Strength (MPa)	Tensile Strength (MPa)
70	All	210	450
80	All	480	520

Fastener Marking Requirements

• Manufacturer's identifier (logo or code)
• Material grade (e.g., 304, 316)
• Property class (if required)

My Experience
For a customer supplying bolts to a chemical plant, we provided 316 bar meeting ASTM F593² Group 2, property class 70. The bolts were marked with the manufacturer's ID and "316".

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Conclusion

304 and 303 are used for general fastener manufacturing. 316 is for marine applications. 410 is for high-strength bolts. Stainless steel bars are hot rolled and cold finished. ASTM F593¹ is the standard for stainless steel bolts².

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