Bolts and Nuts for Metal Joints and Structural Connections
Already know the size you need? Or working out which strength grade applies?
Bolted connections are the standard in steelwork, equipment installation and joinery. Unlike cross-head screws, hex bolts are tightened with a spanner or impact gun and can be disassembled repeatedly without damaging the head.
Hex bolt (HEX) - six-sided head, spanner tightened. Strength grades: 4.6 (general use), 8.8 (standard structural steelwork), 10.9 and 12.9 (dynamic loads). Grade is stamped on the head.
Carriage bolt - domed head with no spanner grip, tightened from the other side with a nut. For wood-to-metal or wood-to-wood joints.
Hex nuts and nylon-insert locknuts (Nyloc) - standard HEX nut and Nyloc which won't vibrate loose.
Washers - flat and spring (split ring). Flat washer distributes load. Spring washer prevents self-loosening under vibration.
Material: galvanised (interior and covered outdoor use), stainless A2/A4 (wet environments, food industry, marine).
8.8 means tensile strength 800 N/mm² and yield strength 80% of that (640 N/mm²). Standard grade for general structural steelwork. Grade 4.6 is for light general use. Grades 10.9 and 12.9 are for dynamic loads and pre-tensioned bolts.
Stainless A2 for exposed outdoor structures, damp rooms, plumbing. Stainless A4 (acid-resistant) for marine environments and food industry. Galvanised is fine for dry interiors and covered outdoor structures.
Yes, with limits. The nylon insert loses effectiveness after 1-2 removals. For critical joints replace the Nyloc at every disassembly. For general non-critical use - 2-3 tightenings is acceptable.
Flat washer under the bolt head and under the nut - distributes load, protects the surface. Spring washer (split ring) under the nut - prevents self-loosening under vibration. Classic stack: flat washer + spring washer + nut.
Diameter comes from structural calculation or design codes (EN 1993 for steel structures). For general non-structural joints: 8-10mm bolt for light loads below 500 kg, 12-16mm for medium loads, 20mm and above for load-bearing structure.
