Bolt

(1) Hexagonal bolts
M6~M24 (commonly used M10, M12, M16).
(2) High-strength bolts
8.8, 10.9 (such as M16×50, M20×60).
(3) Flange bolts
M12~M30 are commonly used, and the length must penetrate the flange thickness (such as flange thickness 20mm, select bolt length 50mm).
(4) Expansion bolts
M8~M16, length 50~150mm (select according to steel pipe load and base material strength).
(5) U-bolts
Specification example: M10×Φ50 (bolt diameter 10mm, suitable for steel pipe outer diameter 50mm).

1. ISO standard
ISO 4014: Hexagon head bolts (A/B grade, equivalent to GB/T 5782)
ISO 4017: Hexagon head full thread bolts (equivalent to GB/T 5783)
ISO 898-1: Bolt mechanical properties standard (4.8~12.9 grade)

2. German standard
DIN 931: Hexagon head partial thread bolts
DIN 933: Hexagon head full thread bolts
DIN 6914: High-strength steel structural bolts (10.9 grade)

3. American standard
ANSI B18.2.1: Hexagon head bolts (English series)
ASME B16.5: Pipe flange bolt size standard (for flanges)
ASTM A193: Alloy steel bolts for high temperature and high pressure (such as B7/B8 for petrochemical pipelines)
ASTM A320: Low temperature bolts (L7/L43, suitable for low temperature steel pipes)

Classification by use
Ordinary bolts: used for general connections, such as hexagonal bolts.
High-strength bolts: used to bear large loads (such as steel structure connections), requiring pre-tightening force (such as grade 8.8, grade 10.9).
Expansion bolts: used for brittle materials such as concrete, fixed by friction generated by expansion.
Anchor bolts: pre-buried in the foundation to fix large equipment.

Classification by head shape
Hexagonal head bolts: the most common, easy to operate with a wrench.
Hexagon socket bolts (such as ISO 4762): with hexagonal holes on the head to save space.
Round head/square head bolts: round heads are beautiful, and square heads are anti-rotation.

Classification by thread type
Coarse thread (such as M10): standard thread, easy to disassemble and assemble.
Fine thread (such as M10×1.25): small pitch, good anti-loosening, used for precision connection.

Construction: High-strength bolts for steel structures (such as friction-type connections).
Automobiles: Engine connecting rod bolts (need to be precisely preloaded).
Household appliances: Small self-tapping bolts (directly tap into plastic or thin metal).