In precision machining, many engineers and buyers often wonder:

“Why do materials like SUS303, A6061, or SCM435 have different codes depending on the supplier or drawing revision, even though they are supposedly the same material?”Even drawings from the same customer may use different material designations in different years.In reality, a material code is not just a “label.”It reflects manufacturing processes, quality requirements, specific material characteristics, and even functional differences.
Understanding these distinctions helps prevent miscommunication and allows faster evaluation of cost and lead time.Here, we break down why the same material name can have different material codes from four key perspectives.

🔍 Same Material Name ≠ Same Specifications

Even if two materials share the same name, their composition, condition, hardness, and machinability may differ.
These differences affect tool wear, machining time, and surface finish, which is why factories must separate them by material code to prevent mix-ups.

🔹 Stainless Steels (SUS Series)

• SUS303 / 303B: Standard grade, average machinability

• SUS303Cu: Copper added for better machinability and shorter cycle time

• SUS303F: Free-cutting grade ideal for mass production

• SUS304 / 304L / 304F: Strength, corrosion resistance, and machinability vary; 304F is free-cutting, 304L is low-carbon

🔹 Alloy Steels (SCM Series)

• SCM415 / 435 / 440: Dramatic differences in strength, heat-treat hardness, and machinability

• S45C / S50C: Different carbon content → different tool wear and strength

🔹 Aluminum Alloys (A6000 Series)

• A6061-T6: Most common and stable

• A6061-T651: Stress-relieved; less deformation

• A7075: High strength but hard to machine; short tool life

🔹 Copper Alloys

• C3604: Excellent free-cutting performance

• C2680: Harder; faster tool wear

• CAC406: High strength but poor machinability

• C1020 (Oxygen-free copper): Very conductive but extremely sticky to cut

🔹 Titanium Alloys

• Ti-6Al-4V (Grade 5): Very high strength and extremely difficult to machine

• Grade 2: Softer and easier to process

Even small differences in material properties can change machining difficulty, cycle time, and cost—making separate material codes essential.

🛠️ Different Machining Processes Require Different Material Codes

Even for identical shapes, machining routes may differ, so materials need to be tracked separately.

• Swiss-type automatic lathes: Ideal for long bar stock and mass production

• Turn-mill composites: Required for parts needing both turning and milling

• CNC lathes: Different tooling and process flow

Since tooling paths, fixtures, machining time, and cost differ greatly,factories manage these differences with separate material codes for safety and traceability.

✏️ Minor Design Changes → Different Material Code

Even a 0.05 mm difference can significantly alter machining procedures.

• Tighter tolerances → more measurement and inspection

• Finer surface finish → tool changes or longer machining time

• Added chamfers or grooves → new tools and toolpaths required

To avoid version mixing and quality issues, ISO and AS9100 recommend distinguishing specifications with separate codes.

🎯 Different Applications Require Separate Material Codes

Even if the shape and material name are the same, different uses require separate material codes:

• Version A → Mass production

• Version B → Prototyping

• Version C → Inspection jigs or testing

• Version D → For different customers with different requirements

Use-case changes affect inspection criteria, lead time, and cost.Thus, material codes ensure clear and reliable traceability.