Screws of fasteners

1. classification
According to head shape and driving mode
Pan head screw: where the head is protruding and requires large force.
Countersunk head/pan head screw: the head is flush with the surface of the workpiece, which is beautiful and reduces interference.
Socket head cap screw: the head contains a hexagonal groove, which is used to connect scenes with high strength (such as mechanical structure).
Slotted/Cross recessed screw: universal type, convenient for common tool operation.
By functional characteristics
Machine screws
Standard thread, need to pre tap the threaded hole, used for the connection of instrument and equipment shell.
Set screw
Conical or flat end design, fix the relative position of the parts (e.g. prevent the shaft from sliding with the hub), rather than the connection effect.
Tapping screw
The front end is sharp, and it can cut and form threads directly on soft materials (plastic, thin metal), without prefabricating holes.
Wood screw
With deep thread and large pitch, it is specially used for wood connection.
Locking screw
Special structure (such as nylon insert and deformed thread) to prevent looseness caused by vibration.
2. key parameters of screws
Thread: including tooth type, nominal diameter, number of lines, pitch and direction of rotation. When the internal and external threads are used in pairs, these elements must be consistent; Head type and groove type.
3. screw material
Carbon steel: high strength, good wear resistance, low cost, suitable for general non corrosive environment, but easy to rust, wet environment requires coating treatment,
Stainless steel: with strong corrosion resistance and high temperature resistance, it is suitable for humid and corrosive environments, such as the chemical industry.
Titanium alloy: light weight, high strength, corrosion resistance, suitable for aerospace, chemical, marine and other environments, but the cost is high.
Aluminum alloy: light weight, excellent thermal conductivity and conductivity, widely used in automotive, electronic equipment and other fields, with low strength and hardness.
Brass: with good processability, electrical conductivity and thermal conductivity, it is widely used in household, construction and other fields, but it is easy to be corroded,
4. purpose
The core function of the screw is connection, fixation and positioning. The application scenarios include:
Mechanical manufacturing: assembling equipment shell and gearbox; Adjust part position.
Electronics and appliances: fix the circuit board and heat sink.
Automotive/Aviation: connect interior trim; Engine component positioning.
Architecture and home: install doors, windows and furniture (wood screws/self tapping screws); Steel structure connection (high-strength bolt screw composite structure).
5. summary
As one of the most common fasteners, screws are better than bolts in the scene of low disassembly frequency or limited space due to their characteristics of directly screwing into the workpiece without nut matching. When selecting, it is necessary to comprehensively consider the material characteristics (such as self tapping screws used for soft materials), stress requirements (hexagonal socket screws with strong bearing capacity) and anti loosing requirements.