Trace every bolt and nut box to its wire rod coil, heading run and plating batch.

A fastener plant buys wire rod in coil. Drawing brings it down to blank diameter, then headers form the head and rollers cut the thread, and the parts are hardened, tempered and coated for stock or for a buyer’s drawing. Both routes share the same machines.

Each carton gets a lot number that reaches back through the plater, the furnace load and the heading run to the coil heat number. A field failure then points at one coil. Tensile, proof load, hardness and coating thickness stay with the lot. Nothing is looked up later. Your own bolt sizes, property classes and plating or galvanising routes decide how the trail is laid out.

Orders come in two kinds. Catalogue hex bolts, set screws and flange nuts are made to stock in standard sizes and classes like 8.8 and 10.9, while special parts follow a customer drawing. Wire rod arrives in coil with a mill certificate for chemistry and grade, and it is annealed, pickled, phosphate coated and drawn to the blank diameter the header needs.

On the floor, a multi-station header shears blanks and forms heads in several blows, then thread rollers press the thread between flat or round dies. Hardening follows. Parts pass through a mesh-belt furnace and an oil quench, then a tempering oven that sets the property class. The lab checks Rockwell hardness, tensile strength and proof load against the class. Zinc flake or electroplate follows, with a hydrogen embrittlement bake where the class needs it. Optical sorting removes mixed, cracked or burred parts before the rest are counted into cartons and drums that are weighed, labelled and stacked against the order.