DIN 557 Carbon Steel Square Nuts | Product Grade C, Metric Coarse Thread

Product Introduction
Metric square nuts manufactured to DIN 557, product grade C. The square external drive profile provides a positive wrenching surface and resists rotation when seated in a matching square recess or channel. Thread sizes M5 to M20 in metric coarse pitch. Available in carbon steel property classes 4, 5, 8, 8.8, and 10, plus stainless steel A2-304 and A4-316. Surface finishes include zinc plating, hot-dip galvanizing, black oxide, and plain uncoated.

Material & Mechanical Properties
Carbon steel grades conform to ISO 898-2. Class 5 is standard for general applications; class 8.8 is specified where higher proof load is required. Stainless steel versions meet ISO 3506-1: A2-70 for general corrosion resistance, A4-80 for enhanced resistance in chloride and marine environments. Mechanical values are certified by lot with heat-number traceability.

Geometry & Thread
Square body dimensions follow DIN 557. Key reference values: M5 width across flats 8 mm, height 4.0 mm; M8 width 13 mm, height 6.5 mm; M10 width 16 or 17 mm, height 8.0 mm; M16 width 24 mm, height 13.0 mm; M20 width 30 mm, height 16.0 mm. The full coarse thread provides engagement along the complete nut height, suitable for through-bolt assemblies where thread length permits.

Corrosion Protection
Standard finishes: electroplated zinc with clear, yellow, or blue passivation (Cr(VI)-free options available); thick-layer zinc plating (8 µm); hot-dip galvanizing for structural exposure; black oxide for appearance and mild corrosion resistance; and plain uncoated for applications where coating is not required or secondary protection is applied.

Application Suitability
Insert nuts in injection-moulded plastic components, where the square geometry prevents rotation within the moulded cavity. Slide-in nuts for profile rails and cage nut assemblies. Agricultural machinery including tractor components, seeders, and attachments. The product grade C tolerance class suits non-precision applications where a robust, low-cost square nut is specified.