Bolt talk

27 October 2009

Common standard commercial grade bolt and nut is grade 4.6 this is manufactured from mild steel with a hexagonal shaped head and often has 4.6 stamped on the face of the bolt/bolts. A lower quality bolt may have 2.6 or nothing stamped on the head. The standard thread length for Australian bolts is normally 2.5 x the diameter of the bolt, this rule applies to marine grade and high tensile and mild steel also. Available measured and named in both metric bolt and imperial bolt sizes. The most common and best priced is usually metric coarse (standard). Other bolt/thread sizes are metric fine,metric extra fine and metric coarse. Metric coarse is most common and cheaper to manufacture, and also imperial bolts unc, unf and whitworth to name a few. Shorter bolts tend to be fully threaded and are referred to as set screws. The same goes for stainless steel bolts.

Basicly a hex head set screw is any fully threaded hex head bolt. All are available in a range of materials all suitable for different applications. Some material examples would be high tensile, mild steel and stainless steel. there are many different varieties of high tensile mild steel and stainless steel fasteners, also many varieties of coatings and alloys. Some common examples of materials and coatings would be zinc plated, galvanized, 304 stainless steel,316 stainless steel, and 410 grade stainless steel.

Some other types of bolts are cup head bolts and coach screws both are usually mild steel or stainless steel bolts and are generally used for bolting timber. Both cuphead bolts and coach screws are available with zinc coating or hot dipped galvanized. The stainless steel bolt variety has a superior resistance to corrosion and is best for outside applications and the zinc bolts that cost less to manufacture are best in applications that are out of the weather gavanized bolts are somewhere in the middle.

A very common high tensile metric bolt is referred to as class 8.8, less common metric high tensile bolt is class 10.9 sometimes called a catapiller bolt.

Imperial high tensile bolts mainly unc (united national coarse) and unf (united national fine) are labeled grade 5 and grade 8.

Stronger than high tensile bolts is a socket head cap screw, these are similar to a bolt and have an internal hex drive. Tightened or removed with an allen key or hex key.