Fasteners serve as the "industrial cornerstone" for connecting and securing mechanical components, playing a vital role across industries from automotive maintenance to high-end equipment manufacturing, household appliances to aerospace systems. Core components like screws, bolts, and nuts not only form the foundation of assembly processes but also directly determine equipment stability, safety, and service life. High-quality fasteners effectively prevent failures caused by loosening or breakage, particularly in advanced manufacturing and specialized industries where they act as critical safeguards for maintaining precision equipment operation and adapting to extreme environments. This article provides comprehensive professional guidance through categorization of fasteners, criteria for high-quality evaluation, selection principles, and multi-scenario applications (including advanced manufacturing and specialized sectors).

I. Core classification of fasteners: classified by structure and use

There are various types of fasteners, which can be divided into two categories according to the connection principle: thread and non-thread. Among them, thread is the most widely used in various industries because of its detachability and strong adaptability. The core characteristics and uses of the categories are as follows:

(1) Thread fasteners: "thread engagement" to achieve accurate fixation

Thread fasteners transmit torque through the engagement of internal and external threads, can be disassembled repeatedly as required, and can be used to connect light and thin parts to heavy structures. The details of the core categories are as follows:

(2) Non-threaded fasteners: irreversible fixation is achieved by "physical interlocking/pressing"

Non-threaded fasteners do not need thread engagement, and are fixed by structural deformation and interference fit. They are suitable for scenarios that do not require disassembly or rapid assembly. The core categories are as follows:

Rivet: divided into hollow rivet, solid rivet and blind rivet. Rivet is joined by extrusion deformation and can not be disassembled. It is suitable for body sheet metal connection in auto repair, skin fixation in aerospace, and shell splicing in medical equipment;

Pin: cylindrical pin (positioning), conical pin (anti-rotation), elastic pin (buffering), through the interference fit to limit the displacement of the parts, suitable for machine tool guide rail positioning, engine crankshaft and flywheel connection, precision instrument bearing seat positioning;

Clamp: plastic/metal material, which can be inserted into the installation hole through elastic deformation and is easy to disassemble. It is suitable for car wire harness fixing, internal wiring arrangement of home appliances, and shell splicing of electronic equipment.

II. Core criteria for determining high quality fasteners

High quality fasteners need to meet strict requirements in three dimensions of material, precision and performance. Especially in high-end manufacturing and special industries, small defects may cause major safety risks. The specific determination criteria are as follows:

(1) Material: determines strength, corrosion resistance and environmental adaptability

The requirements for material strength and corrosion resistance vary greatly in different scenarios. High quality fasteners should meet the industry material standards and avoid using inferior

Key Points: High-quality carbon steel fasteners must undergo "tempering treatment (quenching + high-temperature tempering)" to ensure uniform strength. Stainless steel fasteners should clearly indicate their material grades (e.g., 304 corresponds to A2, 316 corresponds to A4) to prevent the use of rust-prone 201 stainless steel as a substitute for 304. Titanium alloy and high-temperature alloy fasteners require submission of material inspection reports to confirm compliance with specialized industry standards.

(2) Precision: affects assembly fit and torque transmission efficiency

High precision is the core premise of fastener adaptation to precision equipment, which is mainly reflected in two aspects: thread precision and geometric tolerance:

Thread accuracy classification: Per China's GB/T 197 or ISO 965 standards, threads are categorized into three grades: Precision (4H/5g), Medium (6H/6g), and Rough (8H/8g). High-end manufacturing sectors like machine tools and medical devices require Precision-grade threads with complete thread profiles free of burrs. These threads must be easily screwed into by a common thread gauge and not exceed two threads when measured by a stop gauge. For automotive repair and general machinery applications, Medium-grade threads ensure smooth meshing.

Geometric tolerances: The coaxiality error between the head and rod must be ≤0.1mm (to prevent uneven force distribution during tightening); the perpendicularity error between the head plane and rod axis must be ≤0.5° (to ensure proper component surface contact and avoid localized damage); the straightness error of the rod must be ≤0.1mm/m (to prevent installation jamming, especially suitable for automated assembly lines).

(3) Performance: meet the extreme requirements of strength, anti-loosening, weather resistance

The performance of fasteners should be adapted to the force and environmental characteristics of the scene. The core performance indicators and requirements are as follows:

Tensile and yield strength performance: The core specifications are "tensile strength" and "yield strength". For example, Grade 8.8 bolts must have a tensile strength ≥800MPa and yield strength ≥640MPa; Grade 12.9 bolts require tensile strength ≥1200MPa and yield strength ≥1080MPa. During testing, specimens must exhibit "ductile fracture" (with rough fracture surfaces and necking) to exclude "brittle fracture" (showing smooth fracture surfaces and sudden failure).

Anti-loosening performance: special anti-loosening design is required in high vibration scenarios (e.g., wind power, aviation), and common methods include:

Structural anti-loosening: anti-loosening nut with non-metallic insert (increased friction), Spiber thread (special tooth type, reverse lock), threaded bolt with toothed flange surface (locking parts surface to prevent slipping);

Process anti-loosening: surface coating with removable anti-loosening glue (e.g., Leta 243), permanent anti-loosening glue (e.g., Leta 272, suitable for high temperature scenarios), hot-dip galvanized/dacro treatment (to improve surface friction).

Weather resistance: exposed or harsh environment needs to be reinforced anticorrosion, common surface treatment process and effect:

Hot-dip zinc: zinc layer thickness ≥85μm, neutral salt spray test resistance ≥500 hours, suitable for auto repair chassis, outdoor photovoltaic bracket;

Dacro (zinc-chromium coating): salt spray resistance test for more than 1000 hours, no risk of hydrogen embrittlement, suitable for high strength bolts for high-end manufacturing (such as machine tool spindle bolts), engine parts for special industries;

Electrophoretic coating: coating thickness 15-30μm, both anti-corrosion and beautiful, suitable for body appearance parts, medical equipment shell fasteners;

Dulling treatment: special for stainless steel, forming oxide protective film, acid and alkali corrosion resistance, suitable for new energy battery pack, Marine equipment.

III. Selection and use points of high quality fasteners

The selection should follow the principle of "scenario demand → performance matching → cost matching" to avoid "using large materials for small purposes" or "insufficient strength", and avoid operational mistakes to ensure assembly quality.

(1) Selection: accurately match according to the characteristics of the scene

Select according to strength of force:

Low stress scenarios (interior panels, home appliance casings): Select grade 4.8 carbon steel screws and self-tapping screws, low cost and meet the requirements;

Middle load scenario (chassis bracket, machine tool panel): select grade 8.8 alloy bolt, A2-70 stainless steel nut, balance strength and corrosion resistance;

High force application scenarios (engine cylinder head, wind power flange, aviation structural parts): Select grade 10.9 / 12.9 high strength bolts and titanium alloy fasteners, which need to be tightened with torque wrench according to the specified torque to ensure load transmission.

Select according to the degree of environmental corrosion:

Dry environment (machine tool inside, home appliance inside): select carbon steel galvanized fasteners, cost performance is high;

Damp/oil environment (chassis, gearbox, Marine equipment): Select A4-80 stainless steel (316), Dacro treated alloy bolts, anti-rust and oil erosion;

Extreme environment (high temperature, strong acid and alkali, nuclear industry): select high temperature alloy, titanium alloy fasteners, such as aviation engine nickel-based alloy bolts, titanium alloy screws for medical devices.

Select according to assembly scene and precision requirements:

Narrow space (buss fixing, inside precision instrument): select hex socket set screw and thin head screw to avoid tool interference;

Automated assembly line (automobile factory, electronic industrial park): select bolts with guide head and standardized screws to improve assembly efficiency;

Frequent disassembly scenarios (repair cover plate, test panel): select cross/one-way screws to avoid hex socket (requires special tools);

Precision equipment (medical equipment, aviation equipment): Select precision grade (4H/5g) threaded fasteners to ensure assembly gap ≤0.02mm.

(2) Use: avoid operation mistakes and ensure assembly quality

Pre-treatment:

Clean the oil and rust on the surface of fasteners before installation, and blow impurities in the threaded holes with compressed air to avoid meshing jam;

Non-self-driven screws need to drill a bottom hole in advance, and the diameter of the bottom hole should match the thread specification (e.g., M8 screw pre-drill 6.8mm bottom hole, M10 screw pre-drill 8.5mm bottom hole) to prevent the matrix from cracking;

Stainless steel fasteners should be coated with anti-biting agent (such as copper based grease) when installed to avoid thread bite (stainless steel is prone to cold welding).

Torque control link:

Key parts (tire, engine cylinder head, wind power flange) must be tightened with torque wrench according to the technical manual torque. For example, tire bolt torque 80-120N・m, engine cylinder head bolt torque 50-80N・m (adjust according to different models), over-tightening is easy to cause bolt fracture, insufficient torque is easy to loosen;

The threads of the repeatedly disassembled fasteners should be checked for wear. If "thread slip" (deformation of threads and inability to bite) occurs, they should be replaced immediately and not used further (especially in high force scenarios).

Fireproof reinforcement link:

Vibration frequent scene (drive shaft, suspension, wind power equipment): in addition to selecting anti-loosening nut, spring washer (buffer vibration) and flat washer (increase the force area, prevent parts crushing) are added. For example, wind power flange bolt should be used with anti-loosening glue and spring washer at the same time;

High temperature scenario (exhaust pipe, engine combustion chamber): select high temperature resistant anti-loosening glue (such as Letai 272), high temperature alloy fasteners, avoid high temperature failure of anti-loosening performance.

IV. Typical scenarios: High quality fastener applications in many industries

(1) Auto repair industry: ensure the safe operation of vehicles

Engine cylinder head bolt: the material is grade 12.9 alloy structural steel, surface dacro treatment, tensile strength ≥1200MPa, need to follow the "partial diagonal tightening" process (first to 50% torque, 5 minutes after static, to 100% torque), to prevent cylinder head deformation leading to seal failure;

Tire bolt: the material is grade 10.9 high strength carbon steel, surface hot-dip galvanized, salt spray test is more than 500 hours, install in the "crossing order" to tighten, avoid uneven force on the rim caused by shaking.

(2) High-end manufacturing: support the stable operation of precision equipment

Machine tool spindle bolt: the material is grade 12.9 alloy bolt, thread precision 4H/5g, geometric tolerance coaxiality ≤0.05mm, it needs to be tightened with hydraulic wrench at 150-200N・m torque to ensure that the spindle and frame have no gap, avoid processing precision deviation;

Wind power equipment flange bolt: the material is 10.9 grade high strength alloy, surface dacro treatment, salt spray test for more than 1000 hours, a single bolt needs to withstand more than 50kN pull, after installation, ultrasonic detection of thread engagement quality is required to prevent loosening caused by wind load.

(3) Special industries: suitable for extreme environment and high safety requirements

Aerospace:

Aerospace structural bolt: Made of titanium alloy with surface passivation treatment, featuring tensile strength ≥1100MPa and 40% lighter than carbon steel, meeting spacecraft lightweight requirements. Threaded precision 4H/4g with assembly clearance ≤0.01mm, ensuring stable operation in space's zero-gravity environment and temperature fluctuations ±200℃.

Medical devices:

Surgical instrument connecting screw: the material is 316L stainless steel (medical grade), the surface is electrolytic polishing, no dead corners and easy to clean, acid and alkali corrosion resistant (suitable for disinfection scene), thread precision 5H/5g, ensure that the instrument is not loose in the joint, avoid failure during surgery.

New energy storage:

Battery pack bolts: Made of A4-80 stainless steel (316), with an insulation coating thickness ≥20μm and salt spray resistance test duration ≥1500 hours, designed for humid battery environments. After installation, use a gas-tightness tester to ensure IP67 waterproof rating to prevent electrolyte leakage.

While high-quality fasteners may appear as "small components", they serve as the "cornerstone" for equipment safety across industries. From routine maintenance in automotive repair to precision assembly in advanced manufacturing, and extreme environment adaptation in specialized fields, their material composition, dimensional accuracy, and performance directly determine equipment stability, operational safety, and service life. Professionals must master the comprehensive knowledge framework of "classification characteristics → evaluation criteria → selection methods → scenario-specific adaptation". When selecting fasteners, practitioners should avoid both "excessive strength" and "insufficient performance", while strictly controlling torque application and anti-loosening procedures during operation. This approach maximizes fastener effectiveness, reduces equipment failure risks, and ensures production safety across industries.