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Common strength grades for carbon steel screws

Specifications of American screws, such as 6 # -32 * 3/8, 6 # is the outer diameter of the tooth, which is close to 3.5mm; 32 is 32 teeth per inch of thread length (equivalent to the pitch of the metric screw); 3 / 8 is the length of the screw (specifically the same as the metric screw).

There are 2 formulas to keep in mind here: tooth outside diameter A # = (Ax0.013 + 0.06) x25.4 (mm), 1 inch = 25.4mm.

Among them, 2 # = 2.2mm, 4 # = 2.9mm, 6 # = 3.5mm, 8 # 4.2mm, 10 # = 4.8mm are data to be memorized. The number of teeth corresponding to each type of screw must also be memorized: 2 # -56, 4 # -40, 6 # -32, 8 # -32, 10 # -24, 1 / 4-20, 5 / 16-18 , 3 / 8-16, 1 / 2-13 (American standard teeth).

Note: American UNC teeth are standard teeth and UNF are fine teeth. We default coarse teeth to standard teeth.

Material: The most common materials are: carbon steel, stainless steel, stainless iron, copper, aluminum, etc.

Carbon steel is divided into low carbon steel (such as C1008 / C1010 / C1015 / C1018 / C1022), medium carbon steel (such as C1035), high carbon steel (C1045 / C1050), and alloy steel (SCM435 / 10B21 / 40Cr).

Generally, C1008 materials are made of ordinary grade products, such as 4.8 grade screws and ordinary grade nuts; C1015 is generally used as eye bolts; C1018 is generally used as machine screws, of course, it is also used as self-tapping screws; C1022 is generally used as self-tapping screws C1035 hits 8.8 screws; C1045 / 10B21 / 40Cr hits 10.9 screws; 40Cr / SCM435 hits 12.9 screws.

Stainless steel has SS302 / SS304 / SS316 as the most common. Of course, there are also a lot of SS201 products, even products with lower nickel content. We call them non-authentic stainless steel products; the appearance looks similar to stainless steel, but the corrosion resistance is much different.

Strength grade: The strength grade mainly refers to carbon steel fasteners.

Common strength grades for carbon steel screws are: 4.8, 5.8, 6.8, 8.8, 10.9, and 12.9. The corresponding nuts are: 4th, 6th, 8th, 10th, and 12th.

Generally, screws below grade 8.8 are called ordinary screws, while those above grade 8.8 (including grade 8.8) are high-strength screws. The difference is that high-strength screws need to be quenched and tempered.

Surface treatment: The surface treatment is mainly to increase the anti-corrosion performance, and some colors are also taken into consideration, so it is mainly for carbon steel products, and generally requires surface treatment.

Common surface treatments are: blackening, galvanizing, copper plating, nickel plating, chrome plating, silver plating, gold plating, Dacromet, hot-dip zinc, etc .;

There are many types of galvanization, including blue and white zinc, blue zinc, white zinc, yellow zinc, black zinc, green zinc, etc.At the same time, it is also environmentally friendly and not environmentally friendly.Each plating has a variety of coating thicknesses to meet different requirements. Salt spray test effect.

This is a general parameter for fasteners, but there are still many to elaborate.For example, the nominal diameter of the threads in the fastener specifications is divided into many, such as ordinary threads (M), pipe threads (C, Rc, Rp, R), trapezoidal thread (Tr), and serrated thread (B).