- Torx screw,torx machine screw,torx self tapping screw
- sales@jlfastener.com
round head machine screw
Torx machine screw
Material: 304 plum slot, flat round head machine screw, ISO7380
- Description：Hexagon socket button head machine screws with a pin (commonly referred to as "internal hexagon button head machine screws with a pin") combine the low-protrusion feature of the button head and the an
From the perspective of head dimensions, the core parameters of the button head (designated as "P") must comply with the GB/T 818.1 or ISO 7045 standard. The head diameter (dₖ) must match the screw specification. Taking the common M3 specification as an example, the standard range of the head diameter is 5.5-6.0mm, with a tolerance not exceeding ±0.15mm; for the M4 specification, the head diameter is 7.0-7.6mm. This ensures sufficient pressure-bearing area while preventing it from exceeding the reserved installation space of the equipment. The head height (k) is also strictly restricted: the height for M3 is 1.7-2.0mm, and for M4 is 2.0-2.3mm. Excessive height may cause protrusion interference, while insufficient height may weaken the socket strength and affect torque transmission. In addition, the arc radius (r) of the head top surface must match the diameter, usually 1/5 to 1/4 of the head diameter. For instance, the arc radius of an M3 screw is approximately 1.2mm, which ensures a smooth transition of the head and avoids scratching components during assembly.
The socket dimension is crucial for the "hexagon socket with a pin" structure and must adhere to the GB/T 2671.1 or ISO 4757 standard. The socket is designated as "T" (hexagon with a pin), featuring 6 notches and a central cylindrical pin (a mistake-proof design that only fits hexagon wrenches with a hole). Taking the M3 screw as an example, the standard value of the socket's opposite side distance (s) is 2.0mm with a tolerance of ±0.05mm; the socket depth (t) is 1.0-1.2mm, which must be sufficient for the wrench to insert and prevent "slippage" (tool slipping out of the socket). The diameter (d₁) of the central cylindrical pin is approximately 0.5mm, with a height equal to the socket depth. An excessively large or small pin diameter will result in improper wrench fitting or failure of the mistake-proof function. It is worth noting that the socket dimension must match the head height. For example, when the head height of an M4 screw is 2.0-2.3mm, the socket depth should be controlled at 1.2-1.4mm to prevent the socket bottom from penetrating the head.
The screw shank and thread dimensions must comply with GB/T 196 (General Purpose Metric Threads) and GB/T 3103.1 (Thread Tolerances) standards. The shank diameter (d) refers to the screw specification (e.g., M3, M4), with a common tolerance class of 6g (for external threads) to ensure fitting accuracy with nuts or threaded holes. The thread length (lₜ) is divided into full thread and partial thread: the thread length of full-thread screws is ≥90% of the total shank length (e.g., an M3×10 full-thread screw has a thread length ≥9mm); the thread length of partial-thread screws is determined by the specification—the minimum thread length for M3 is 6mm, and for M4 is 8mm. The unthreaded section (smooth shank) has a slightly smaller diameter than the major thread diameter to reduce assembly resistance. The total shank length (l) is labeled as "specification × total length" (e.g., M3×10), where the total length refers to the distance from the top of the head to the end of the shank, with a tolerance of ±0.2mm (for lengths ≤10mm) to ensure the screw can be fully screwed into the threaded hole during assembly.
In addition, details must be noted for dimension labeling and selection adaptation. A complete dimension label should include "specification + socket type + head type + length + standard number", such as "M4×12-T-P-GB/T 818.1". Clear parameters facilitate procurement and assembly. When selecting a screw, its length should be determined based on the thickness of the connected components: if the total thickness of the connected components is 5mm and the threaded hole depth is 8mm, an M4×12 screw is recommended (total shank length 12mm, 8mm screwed into the threaded hole, and the head pressing the connected components). This avoids loose connections due to insufficient length or penetration of the threaded hole due to excessive length. Meanwhile, the head diameter should be determined based on the assembly space. For example, if the reserved head installation space inside the equipment is only 6mm, an M4 screw (head diameter 7.0-7.6mm) is not suitable, and an M3 screw (head diameter 5.5-6.0mm) should be used instead.
The dimension standards of hexagon socket button head machine screws with a pin are essential for ensuring assembly accuracy and connection reliability. Every parameter, whether related to the head, socket, or thread, must strictly comply with national or international standards. In practical applications, it is necessary to accurately match the dimension specifications based on the characteristics of the connected components, assembly space, and service environment. Only in this way can the anti-loosening, anti-slip, and low-protrusion advantages of this type of screw be fully utilized, ensuring the long-term stable operation of the equipment.