Stainless Steel Custom Parts Manufacturing
Stainless steel is the most frequently specified material in our shop. The combination of corrosion resistance, mechanical strength, and availability across dozens of grades makes it a default choice for precision machined parts in fluid handling, instrumentation, chemical processing, and power equipment. We machine all major stainless steel families: austenitic 300 series (303, 304, 316, 316L, 321), martensitic 400 series (416, 420, 440C), and precipitation-hardening grades (17-4 PH).
Each behaves differently under a cutting tool. Free-machining grades like 303 and 416 run at production speeds with clean chip formation. Work-hardening grades like 304 and 316 require slower speeds, sharper tooling, and more rigid setups to hold tolerances and avoid surface damage. We handle both categories across CNC milling, turning, multi-spindle, and Swiss platforms, from single prototypes to high-volume production runs of 100,000+ pieces.
Tolerances range from ±0.001" to ±0.005" depending on grade, geometry, and feature size. Parts are delivered with full documentation including material certifications and dimensional inspection reports.
Stainless steels fall into two main families based on their crystal structure, which determines whether they're magnetic, heat-treatable, and how they behave during machining.
300 series (austenitic) grades contain nickel, which stabilizes a face-centered cubic structure. They are non-magnetic, cannot be hardened through heat treatment, and tend to work-harden during machining, meaning the material gets harder as you cut it. Managing work hardening is the central challenge when machining 304, 316, and similar grades. Free-machining grade 303 adds sulfur to break chips and reduce tool wear, which is why it exists: same corrosion resistance as 304, dramatically easier to machine.
400 series (martensitic and ferritic) grades contain little or no nickel. They are magnetic, can be hardened through heat treatment, and generally machine more predictably than austenitic grades because they don't work-harden as aggressively. Grade 416 adds sulfur for free-machining characteristics. Grade 420 and 440C provide high hardness after heat treatment—440C reaches 58–60 HRC, placing it in the range of some tool steels.
Precipitation-hardening (PH) grades like 17-4 PH occupy a middle ground. They can be machined in a solution-annealed (relatively soft) condition and then age-hardened to high strength afterward. This makes them practical for complex parts that need both tight tolerances and high final strength.
A free-machining austenitic stainless steel modified with sulfur for improved machinability. While offering good mechanical properties and moderate corrosion resistance, it's optimized for high-volume production where machining efficiency is crucial.
Material Cost: 7
Machining Cost: 5
Durability: 7
Corrosion Resistance: 6
Temperature Resistance: 7
Strength-To-Weight Ratio: 6
Typical Tolerances: ±0.002" to ±0.005"
Magnetic: No
The most versatile and widely used austenitic stainless steel. It offers excellent corrosion resistance, good formability, and strong welding characteristics. This general-purpose grade provides outstanding performance in mild to moderate corrosive environments.
Material Properties (Scale 1-10)
Material Cost: 7
Machining Cost: 7
Durability: 8
Corrosion Resistance: 8
Temperature Resistance: 8
Strength-To-Weight Ratio: 6
Typical Tolerances: ±0.002" to ±0.005"
Magnetic: No
A premium austenitic stainless steel containing molybdenum for enhanced corrosion resistance. Its superior performance in aggressive environments, particularly against chlorides and industrial chemicals, makes it ideal for marine and chemical processing applications.
Material Properties (Scale 1-10)
Material Cost: 8
Machining Cost: 8
Durability: 9
Corrosion Resistance: 9
Temperature Resistance: 8
Strength-To-Weight Ratio: 6
Typical Tolerances: ±0.002" to ±0.005"
Magnetic: No
A low-carbon variant of 316 that offers superior welding characteristics by preventing carbide precipitation at weld boundaries. It maintains the same excellent corrosion resistance as standard 316 while providing better intergranular corrosion resistance in welded structures.
Material Properties (Scale 1-10)
Material Cost: 8
Machining Cost: 8
Durability: 9
Corrosion Resistance: 9
Temperature Resistance: 8
Strength-To-Weight Ratio: 6
Typical Tolerances: ±0.002" to ±0.005"
Magnetic: No
A titanium-stabilized austenitic stainless steel designed for high-temperature applications. The titanium addition prevents chromium carbide formation at grain boundaries, making it ideal for applications requiring extended exposure to temperatures between 800-1500°F.
Material Properties (Scale 1-10)
Material Cost: 8
Machining Cost: 8
Durability: 8
Corrosion Resistance: 8
Temperature Resistance: 9
Strength-To-Weight Ratio: 6
Typical Tolerances: ±0.002" to ±0.005"
Magnetic: No
A free-machining martensitic stainless steel designed for high-speed machining. While offering moderate corrosion resistance, its excellent machinability makes it ideal for high-volume production of parts requiring good mechanical properties.
Material Properties (Scale 1-10)
Material Cost: 6
Machining Cost: 5
Durability: 8
Corrosion Resistance: 5
Temperature Resistance: 6
Strength-To-Weight Ratio: 7
Typical Tolerances: ±0.002" to ±0.005"
Magnetic: Yes
A high-carbon martensitic stainless steel capable of high hardness through heat treatment. It combines good corrosion resistance with excellent wear resistance, making it suitable for applications requiring both hardness and moderate corrosion resistance.
Material Properties (Scale 1-10)
Material Cost: 6
Machining Cost: 7
Durability: 9
Corrosion Resistance: 6
Temperature Resistance: 6
Strength-To-Weight Ratio: 8
Typical Tolerances: ±0.001" to ±0.003"
Magnetic: Yes
A high-carbon martensitic stainless steel offering maximum hardness in the 400 series. Its combination of high strength, hardness, and moderate corrosion resistance makes it ideal for bearings, valve components, and other wear-resistant applications.
Material Properties (Scale 1-10)
Material Cost: 7
Machining Cost: 8
Durability: 9
Corrosion Resistance: 6
Temperature Resistance: 6
Strength-To-Weight Ratio: 9
Typical Tolerances: ±0.001" to ±0.005"
Magnetic: Yes
A precipitation-hardening stainless steel that combines high strength with good corrosion resistance. Its ability to achieve high strength through relatively simple heat treatment while maintaining good machinability makes it valuable for critical components requiring both strength and corrosion resistance.
Material Properties (Scale 1-10)
Material Cost: 8
Machining Cost: 7
Durability: 9
Corrosion Resistance: 8
Temperature Resistance: 7
Strength-To-Weight Ratio: 9
Typical Tolerances: ±0.002" to ±0.010"
Magnetic: Yes
Stainless steel handles pressurized, corrosive, and high-purity fluid systems that carbon steel and brass cannot. Grade 316 and 316L are standard in chemical processing lines where chloride exposure or acid contact would pit or corrode lesser alloys. Grade 304 covers less aggressive environments — water systems, compressed air, and general industrial fluid handling. Free-machining 303 is commonly specified for high-volume fittings and connectors where the part won't contact aggressive media. The alloy choice usually comes down to the fluid chemistry. Chlorides and acids push toward 316L. Clean water and steam systems stay on 304. High-volume fittings that see only mild exposure run in 303 for cost efficiency.
Common Applications:
• Valve bodies and valve stems
• Pressure regulator housings
• Flow meter bodies and turbine housings
• Manifold blocks
• High-pressure fittings and adapters
• Sampling system components
• Check valve assemblies
Dimensional stability and corrosion resistance together determine whether an instrument maintains its calibration and accuracy over years of service. Stainless steel provides both. 304 and 316 are standard for gauge housings, sensor bodies, and probe fittings that operate in industrial environments with temperature swings, moisture, and chemical exposure. 17-4 PH is specified when an instrument component doubles as a structural or load-bearing element — it provides both the strength of a high-alloy steel and the corrosion resistance of a stainless. Machinability matters here because instrument components typically require tight tolerances (±0.001" to ±0.002") and fine surface finishes. Grade 303 is often selected for high-volume instrument fittings where the corrosion demands are moderate, because it holds tolerances more consistently at production speeds than 304 or 316.
Common Applications:
• Pressure gauge components
• Sensor housings
• Calibration equipment parts
• Test point adapters
• Instrument fittings
• Temperature probe housings
• High-accuracy gauge parts
Standard off-the-shelf stainless fasteners cover a wide range of applications, but custom stainless steel hardware fills the gap where standard parts don't fit — non-standard thread forms, unusual head configurations, combined features (threaded and press-fit on the same part), or material certifications that off-the-shelf vendors can't provide. 416 and 303 handle the bulk of custom stainless fastener production. Both are free-machining grades that run efficiently at the speeds and feeds high-volume hardware production requires. For applications needing higher corrosion resistance, 304 and 316 fasteners are common but machine more slowly. 17-4 PH covers the high-strength end — custom cap screws, studs, and pins for applications where a standard 304 fastener doesn't have enough tensile or shear strength.
Common Applications:
• Specialty fasteners
• Threaded inserts
• Guide pins and bushings
• Mounting brackets
• Alignment components
• Structural connectors
• High-strength assembly hardware
Stainless steel accounts for more throughput in our shop than any other material family. That volume means our tooling, fixturing, coolant systems, and process parameters for each grade are established and proven.
The main challenge with stainless is work hardening, particularly in austenitic grades (304, 316, 316L). When a cutting tool dwells or rubs instead of cutting cleanly, the surface layer hardens and subsequent passes require even more force, which accelerates tool wear and compromises surface finish. Avoiding this requires sharp tooling, rigid setups, positive cutting engagement, and appropriate feeds. Free-machining grades (303, 416) bypass most of these issues, which is why they exist and why they're specified when the application permits. We produce custom stainless steel precision machined parts from prototypes through high-volume production across four core processes.
Our milling centers (vertical and horizontal, up to 6-axis) handle the geometrically complex stainless work — manifold blocks with intersecting internal passages, sensor housings with thin walls, and valve bodies requiring multiple machined faces in a single setup. Six-axis capability reduces the number of setups per part, which matters on stainless where each re-fixturing introduces positional tolerance stack-up. We run all common grades, with 304, 316, and 303 making up the majority of milling work.
High-volume stainless steel production is where multi-spindle delivers the most value. Fittings, connectors, adapters, and small valve components produced in quantities of 5,000 to 500,000+ run efficiently on our multi-spindle platforms (bars up to 1-5/8", chucking to 6"). Free-machining grades 303 and 416 are the best fit for this process. We also run 304 and 316 on multi-spindle when volumes justify the additional tooling and cycle time investment — the per-part cost advantage of multi-spindle still holds, it just requires more aggressive tool management.
Precision stainless steel turning covers the broadest range of part sizes and complexity in our shop. We turn stainless bar stock up to 4" and chucking up to 20" diameter. Shafts, valve stems, sleeves, fittings, and cylindrical housings in every stainless grade from 303 through 17-4 PH come through our turning cells. For complex stainless steel parts that combine turning with cross-drilling, grooving, or threading, our live-tooling lathes complete the part in a single setup. This matters on work-hardening grades where interrupting a cut and re-fixturing the part creates the conditions that cause dimensional problems.
Small-diameter stainless steel parts (up to 7/8" diameter, 4" length) with tight tolerances and fine surface finish requirements run on our Swiss lathes. Instrument fittings, thermowell tips, miniature valve components, and connector pins are typical work. The guide bushing provides support directly at the cut point, which eliminates the deflection that causes chatter and tolerance loss on small-diameter stainless — especially on 304 and 316 where the material's tendency to grab the tool makes unsupported cuts unpredictable.
Learn more about our machining services and capabilities
Delivering high-quality, consistent s components is a top priority at Spex. Our quality system is built on our ISO 9001:2015 certification, guiding how we work every step of the way. We carefully check parts during production to ensure dimensional accuracy and address the specific needs of machining s.
We apply these same quality standards whether we're making a single prototype or thousands of parts. You can be confident in the results, as each project comes with full documentation, including material certifications, detailed measurement reports, and First Article Inspection Reports (FAIRs). This paperwork clearly shows how your parts meet your exact specifications.
We'd love to hear from you!
Scalable production
Short lead times
Fair prices
ISO-9001 certified
Secondary processes
Range of materials
On-time delivery
75+ years in business
Advanced CNC machining
Rapid prototyping
Stainless steel is a popular choice primarily for its excellent corrosion resistance, making it ideal for parts exposed to moisture, chemicals, or harsh environments. Many grades also offer good strength, durability, temperature resistance, and hygienic properties essential for medical and food processing applications. Plus, its aesthetic appeal is often a benefit for consumer-facing components.
Designing stainless steel parts with machinability in mind can significantly impact production efficiency and cost. Key considerations include: selecting the most machinable grade suitable for the application (e.g., 303 vs. 316), specifying tolerances appropriate for the function (avoiding overly tight specs), incorporating generous radii on internal corners instead of sharp edges, maintaining reasonable wall thicknesses to prevent distortion, and simplifying complex features where possible. Discussing your design with your machining partner early can help optimize it for manufacturability.
Excellent surface finishes, including very fine Ra values, can be achieved on precision machined stainless steel parts. Proper techniques are crucial to avoid issues related to work hardening. We utilize advanced processes to deliver smooth, precise finishes suitable for applications in medical, food processing, and instrumentation industries. We can also coordinate post-machining finishing processes like passivation or electropolishing if required.
Delivering high-quality, consistent stainless steel components is a top priority at Spex. Our quality system is built on our ISO 9001:2015 certification. We carefully check parts during production, using methods suited to stainless steel's properties, ensuring dimensional accuracy and adherence to specifications. These same quality standards apply from prototype to high-volume production runs.
To provide the most accurate quote, please share detailed part drawings or CAD models, specify the exact stainless steel grade required (e.g., 303, 304, 316, 17-4 PH, 416), required tolerances, desired quantity, any critical features, and details on necessary secondary operations if any (like passivation). The more detail provided, the better we can tailor a precise and competitive quote.
