Studs are tools we encounter frequently in our daily lives; different settings and varying installation requirements call for the use of different types of studs. The methods for classifying studs are highly diverse, resulting in a wide variety of styles. Faced with this dizzying array of options, many people often feel overwhelmed and unsure of which specific stud is best suited for their particular application environment and the task at hand. Therefore, this article will introduce the various classification methods and specific types of studs, serving as a useful reference whenever you may need it.
Primary Classification: By Bolt Head
The classification of bolt heads can be further divided into two categories: head shape and tightening method.
Classification by Head Shape
1. Hex Head Bolts
(Pictured: The most common type of hex head bolt-the external hex bolt.)
2. Round Head Bolts
(Pictured: The most common type of round head bolt-the internal hex round head bolt.)
3. Flat Head Bolts
(Flat head bolts are also known as countersunk bolts. Pictured: A common flat head Phillips bolt.)
4. T-Head Bolts and Square Head Bolts
(These two types are quite similar, yet distinct.)* (T-bolts feature a rectangular head, while square-head bolts feature a square head.)
5. Headless Bolts
(The image shows a hex-socket headless bolt.)
6. Double-ended Bolts (Studs)
(The image shows a double-ended bolt.)
Classified by Tightening Method
1. External Hex Bolts
(The image shows a flat-head external hex bolt in its natural finish.)
(Natural-finish bolts do not undergo heat treatment; consequently, they possess a gray exterior with uneven coloration.)
2. Internal Hex Bolts (Socket Head Bolts)
(The image shows a flat-head internal hex bolt.)
3. Slotted Bolts
(The image shows a slotted bolt.)
4. Phillips Bolts
(The image shows a common round-head Phillips bolt.)
5. External Torx Bolts
(The image shows an external Torx bolt.)
6. Internal Torx Bolts
(The image shows an internal Torx bolt.)
(Among these, a specific subset of Torx-head bolts is quite unique. In the case of high-strength bolts, the Torx head is designed to shear off precisely when the applied torque reaches the maximum specified limit. If the head does not shear off, it indicates that the applied torque was insufficient.)
(Additionally, U-bolts are not classified based on their head type. Known in English as "U-bolts," these are non-standard fasteners. Due to their distinct U-shape, they are also referred to simply as U-bolts. Both ends are threaded to accept nuts. They are primarily used to secure tubular objects-such as water pipes-or flat objects-such as automotive leaf springs. They are colloquially referred to as "riding bolts" because the manner in which they secure an object resembles a person riding a horse.)
Second Major Classification: By Material
(Currently, the standard fasteners available on the market are primarily manufactured from three materials: carbon steel, stainless steel, and copper.)
Carbon Steel
We classify carbon steel materials into low-carbon steel, medium-carbon steel, high-carbon steel, and alloy steel based on their carbon content.
1. Low-carbon steel: C% ≤ 0.25%. Primarily used for Grade 4.8 bolts.
2. Medium-carbon steel: 0.25% < C% ≤ 0.45%. Primarily used for Grade 8.8 bolts and similar grades. Internationally, these are typically designated as 1035, CH38F, 1039, 40ACR, and 45; domestically, they are commonly referred to as 35.
3. High-carbon steel: C% > 0.45%. Currently, this material is rarely used in the market.
4. Alloy steel: Formed by adding alloying elements to ordinary carbon steel to enhance specific properties of the material (e.g., 35CrMo, 40CrMo, SCM435). Alloy steel is primarily used in the manufacture of high-performance-grade bolts.
Stainless Steel
Performance Grades: 45, 50, 60, 70, 80.
Classifications include 201, 304, 316, 316L, etc. Simply put, the higher the grade, the better its corrosion resistance and high-temperature resistance. The underlying reason lies in the varying nickel (Ni) content; a higher nickel content results in superior corrosion resistance, including enhanced resistance to corrosion under high-temperature conditions. In terms of mechanical strength, Grade 316 generally outperforms 316L, exhibiting higher yield strength and tensile strength. However, 316L offers superior resistance to both high temperatures and corrosion compared to 316.
Copper
The most commonly used material is brass-a zinc-copper alloy. In the market, H62, H65, and H68 brass are the primary materials utilized for manufacturing standard fasteners. The Third Major Classification: Classification by Performance Grade
Bolts used for structural connections are categorized into over ten performance grades, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, and 12.9. Among these, bolts of Grade 8.8 and higher are manufactured from low-carbon alloy steel or medium-carbon steel and undergo heat treatment (quenching and tempering); these are collectively referred to as high-strength bolts. The remaining grades are collectively referred to as ordinary bolts. The performance grade designation of a bolt consists of two numerical parts, which respectively indicate the nominal tensile strength of the bolt material and its yield ratio. For example, a bolt with a performance grade of 8.8 signifies the following:
1. The nominal tensile strength of the bolt material reaches the 800 MPa level;
2. The yield ratio of the bolt material is 0.8;
3. The nominal yield strength of the bolt material reaches the 640 MPa level (calculated as 800 × 0.8).
The most commonly used high-strength bolts are Grades 8.8 and 10.9, while the most commonly used ordinary bolt is Grade 4.8. In terms of appearance, ordinary bolts typically appear silver, whereas high-strength bolts typically appear black.