Pulling bolts generally use both ends of the set of wire round steel bolts, also known as wall bolts, but also useful flat ends of the long hole with a wedge-shaped iron inserted into the fixed wedge tight. Because the bolts are also a kind of railway fittings, the railroad parts are part of the railway line. The rails mentioned here include rails, sleeper, connecting parts, track bed, anti-climbing equipment, rail brackets and turnouts. As a holistic engineering structure, the rail laying on the roadbed, plays a guiding role in the operation of the train, directly under the enormous pressure of locomotives and their loads. Under the motive force of the train operation, its various components must have sufficient strength and stability, and the instrument ensures that the train operates at the highest speed, safe, smooth and uninterrupted.

Steel structure connection bolts performance grade points 3.6,4.6,4.8,5.6,6.8,8.8,9.8,10.9,12.9 and so on more than 10 grades, of which 8.8 and above bolt material for the low carbon alloy steel or medium carbon steel and processed (Quenching, tempering), commonly known as high-strength bolts, the rest known as ordinary bolts. Bolt performance grade label has two parts of the composition, the wing instrument, respectively, said the bolt material nominal tensile strength and yield ratio.