The basic design of a square bolt is like any other bolt. The square head of the bolt is milled from steel and then it is hardened in a factory. The metal is then soldered together and the end result is a bolt that is strong and long-lasting. The square head is very strong, but it also has some disadvantages. A square bolt can get bent during use or it may break with too much pressure. It also doesn't have as much surface area as a round bolt. Square bolts and washers will need to be pressing into the gas tank to fill holes and they will need to be pressed tightly into the gas tank to prevent leakage.
There are a few different types of square bolt. You can get M1.6 bolts and washers that are made from high carbon steel. These bolts are designed to be very long lasting, but they will wear out quicker. This isn't to say that the bolts won't break when used to replace the M5.2 bolt because there are plenty of.6 bolts and washers that are made from stainless steel. But stainless steel is harder than the other types, so it will probably be longer lasting.
Metric: M1.6-M52 or customized
DIN GB ISO JIS BA ANSI
M1.6-M52 or non-standard as request&design
Carbon steel, mild carbon steel
Plain, Black, Zinc Plate.HDG etc
4.8, 5.8, 6.8, 8.8,10.9,12.9
Usually about 30-45 days
FOB, CIF, CFR, L/C, or others.
Port of Loadinc
Ningbo or Shanghai
TT (30% in advance as deposit, balance before delivery) etc.
Structural Steel; Metal Building; Oil&Gas; Tower&Pole; Wind Energy; Mechanical Machine