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Type 302 is used for screws and self-tapping bolts manufactured by mechanical processing.

To improve cutting performance, type 303 stainless steel contains a small amount of sulfur, which is used for processing nuts from rod materials.

Model 304 is suitable for processing stainless steel screws using the hot upsetting process, such as longer-sized bolts and bolts with large diameters—these may exceed the capabilities of the cold upsetting process.

Model 305 is suitable for processing stainless steel screws using cold heading technology, such as cold-formed nuts and hex bolts.

Type 309 and Type 310 have higher Cr and Ni contents compared to Type 18-8 stainless steel, making them suitable for stainless steel screws used under high-temperature conditions.

Types 316 and 317 both contain the alloy element Mo, which means their high-temperature strength and corrosion resistance are superior to those of type 18-8 stainless steel.

Type 321 and Type 347; Type 321 contains the more stable alloy element Ti, while Type 347 contains Nb, thereby enhancing the material's resistance to intergranular corrosion. Suitable for standard stainless steel components that do not require post-weld annealing or operate at temperatures between 420–1013°C.

The classification of stainless steel screws includes austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and precipitation-hardening stainless steel. The selection of stainless steel screws follows a systematic approach; you can choose based on any aspect you prefer. Through comprehensive consideration across five aspects, the brand, type, specifications, and material standards of the stainless steel screw are ultimately determined.

Austenitic stainless steel: The most fundamental alloying elements of austenitic stainless steel are chromium and nickel. A representative grade is chrome-nickel austenitic stainless steel, which contains approximately 18% chromium and 8% nickel; this type is commonly referred to as 18-8 stainless steel. The ratio of chromium to nickel essentially ensures that the steel structure remains in a stable austenite state.

Iron-type stainless steel: 430 ordinary chromium steel; its corrosion resistance and heat resistance are superior to 410. It is magnetic, but cannot be strengthened through heat treatment. Suitable for applications requiring slightly higher corrosion and heat resistance, and meets the strength requirements of general stainless steel screws.

Martensitic stainless steel: 410 and 416 can be strengthened through heat treatment, with hardness ranging from 35 to 45 HRC. They offer excellent machinability and are suitable for general use as heat- and corrosion-resistant stainless steel screws.

Type 4_16 has a slightly higher sulfur content and is a free-cutting stainless steel. Type 4_20, sulfur content?0.1_5%, with improved mechanical properties; heat treatment can enhance its properties, with a maximum hardness of 5_3~5_8HRC, used for high-strength stainless steel screws.

Precipitation-hardened stainless steel: 1.7–4PH, PH15–7Mo. They can achieve higher strength than conventional Type 18–8 stainless steel, and are thus used for high-strength, corrosion-resistant stainless steel screws.

A-286 – A non-standard stainless steel with higher corrosion resistance compared to the commonly used 18-8 stainless steel, as well as excellent mechanical properties at higher temperatures. It is used for high-strength, heat-resistant, and corrosion-resistant stainless steel screws that can operate between 650~700°C.

Austenitic stainless steel: commonly used grades include 302, 303, 304, and 305, namely the so-called “18-8” type austenitic stainless steel. These four grades exhibit similar corrosion resistance and mechanical properties. The selection basis is the production process of stainless steel screws; the method depends on the size and shape of the screws, as well as the number of productions.

Type 3_02 for machined screws and tapping bolts.

To improve machining performance, a small amount of sulfur is added to 303 stainless steel, which is used for machining nuts made of bar material.

Type 304 is suitable for stainless steel screws processed via hot heading, such as bolts with longer specifications or large diameter bolts, which may fall outside the scope of cold heading processes.

Type 305 is suitable for the cold heading process of stainless steel screws, such as cold-formed nuts and hex bolts.

Models 309 and 310, which have higher Cr and Ni content compared to type 18-8 stainless steel, are suitable for stainless steel screws used at high temperatures.

Types 3-16 and 3-17 contain the alloying element Mo; therefore, their high-temperature strength and corrosion resistance are superior to those of type 18-8 stainless steel.

Type 321 and Type 347: Type 321 contains the relatively stable alloy element Ti, while Type 347 contains Nb, thereby enhancing resistance to intergranular corrosion. It is suitable for stainless steel standard parts that are not annealed after welding or operating at 420–1013℃.