The core difference between the three-piece fish scale expansion screw and the traditional one-piece expansion screw lies in its "split design". It consists of four parts: an externally threaded 螺杆 (screw rod), three independent fish scale-shaped expansion pieces, a conical pull-explosion sleeve, and a hexagonal nut. Among them, the three expansion pieces are symmetrically distributed at 120°, and the surface of the pieces is covered with raised "fish scales" — this design is not decorative, but rather increases the friction coefficient with the hole wall of the base material to avoid "slipping and loosening" after expansion. The inner side of the expansion pieces is processed with inclined clamping grooves, which precisely match the outer conical surface of the conical pull-explosion sleeve, ensuring that the three expansion pieces expand outward synchronously during the pull-explosion process. The tail of the screw rod is provided with an annular groove to fix the position of the expansion pieces and prevent component misalignment during assembly. This structural design not only solves the problem of "easy loosening due to single-point force" of traditional expansion screws, but also realizes uniform pressure distribution on the base material through split expansion, reducing the risk of base material cracking.
Its working principle is based on the dual fastening mechanism of "mechanical pull-explosion + friction locking". The operation process can be divided into four steps: first, drill a mounting hole with a matching diameter in the base material (such as concrete, brick wall) according to the screw specification. The hole diameter must be strictly controlled — usually 1-2mm smaller than the maximum outer diameter of the expansion piece to ensure tightness during initial insertion. Secondly, sleeve the three expansion pieces into the screw rod, assemble with the conical pull-explosion sleeve, and insert the whole into the mounting hole. At this time, the expansion pieces are in a contracted state, only slightly contacting the hole wall through the fish scales. Then, use a wrench to tighten the hexagonal nut, which drives the screw rod to move outward, forcing the conical pull-explosion sleeve to squeeze into the inner side of the expansion pieces. Finally, the inclined surface of the conical pull-explosion sleeve pushes the three expansion pieces to expand synchronously along the radial direction until the expansion pieces are completely attached to the hole wall, and the fish scales are embedded into the surface of the base material to form a "mechanical interlock". At the same time, the pulling force of the screw rod and the radial pressure of the expansion pieces together form a stable fastening system, achieving the effect of "the more force applied, the firmer it becomes".
In terms of performance advantages, the three-piece fish scale expansion screw demonstrates adaptability and reliability that traditional expansion screws cannot match. Firstly, high load-bearing capacity — due to the synchronous expansion of the three expansion pieces, the contact area with the base material is increased by more than 40% compared with the one-piece expansion screw. Combined with the anti-slip effect of the fish scales, its pull-out resistance and shear resistance are significantly improved. According to industry test data, the M12 specification three-piece fish scale expansion screw can achieve a pull-out resistance of 8-10kN in C30 concrete, far exceeding that of the same specification traditional expansion screw (about 5-6kN), which is sufficient to meet the fixing needs of heavy-load equipment such as air conditioning outdoor units, heavy lamps, and steel structure brackets. Secondly, wide base material compatibility — traditional expansion screws are prone to loosening due to "insufficient expansion force" in porous lightweight base materials such as hollow bricks and aerated blocks. However, the split expansion pieces of the three-piece fish scale expansion screw can adjust the expansion range according to the pore conditions of the base material, and through the multi-point interlock between the fish scales and the hole wall, they can still maintain stable fastening in lightweight base materials, solving the industry pain point of "difficult fixing in non-solid base materials". Thirdly, anti-vibration and anti-loosening performance — the 锯齿状 (serrated) structure of the fish scales can effectively resist "reverse displacement" caused by vibration, and even in long-term dynamic load scenarios (such as fixing fans and water pumps), it is not easy to loose due to vibration, which makes it particularly important in industrial equipment installation.
From the perspective of application scenarios, the "strong fastening + multi-base material adaptation" characteristics of the three-piece fish scale expansion screw enable it to cover multiple high-demand fields. In building curtain walls and decoration projects, it is often used for fixing 挂件 (hangers) of stone curtain walls and glass curtain walls. Since curtain walls are exposed to the outdoors for a long time and need to withstand stress caused by wind force and temperature changes, the uniform expansion force of the three-piece fish scale expansion screw can avoid stone cracking, and the anti-slip property of the fish scales ensures that it will not loosen due to vibration during long-term use. In the field of industrial equipment installation, such as fixing heavy machine tools and production line brackets in workshops, its high pull-out resistance can cope with the impact force during equipment operation and prevent equipment displacement. In civil decoration and home appliance installation, for non-solid base materials such as hollow brick walls and gypsum board partitions, when installing heavy objects such as range hoods and water heaters, traditional expansion screws are easy to "crack the wall". However, the three-piece fish scale expansion screw disperses pressure through split expansion, which can not only ensure fastening strength but also protect the wall structure. In addition, in transportation and municipal facilities, such as fixing road monitoring cameras and traffic lights, its anti-vibration and weather resistance (some products are surface-treated with hot-dip galvanizing or dacromet) can adapt to complex outdoor environments and reduce maintenance costs.
However, to give full play to the performance of the three-piece fish scale expansion screw, the following usage points should be noted: first, precise control of the hole diameter — an excessively large hole diameter may cause the expansion pieces to fail to fully interlock, while an excessively small hole diameter may crack the base material. It is recommended to select a drill bit of the corresponding specification according to the product manual, and clean the debris in the hole after drilling to avoid impurities affecting the expansion effect. Second, adaptation of installation depth — the insertion depth of the screw rod must ensure that the expansion pieces completely enter the base material. Generally, it is required that the expansion pieces are fully embedded in the hole, with only the nut and the tail of the screw rod exposed. If the installation is too shallow, the expansion pieces will not expand fully, which will directly reduce the fastening strength. Third, selection of tools and torque — a torque wrench should be used to tighten according to the torque range specified by the product to avoid over-tightening leading to screw rod breakage or base material cracking, and insufficient torque leading to insufficient expansion. Fourth, selection of surface treatment — select products with corresponding surface treatment according to the use environment. For example, in outdoor or humid environments, screws treated with hot-dip galvanizing or dacromet should be selected to prevent rust from affecting service life. Fifth, load assessment — before installation, select the appropriate specification of screws according to the equipment weight and base material strength to avoid potential safety hazards caused by "a small horse pulling a large cart". For example, to fix equipment weighing more than 100kg, it is recommended to use products of M10 and above specifications and conduct a pull-out test.
As an "upgraded version" of the expansion screw family, the three-piece gecko pull-explosion fish scale expansion screw has made up for the performance shortcomings of traditional products through structural innovation and detail optimization, and has become an effective solution to solve the fastening problems in complex base materials, high-load, and vibration scenarios. With the development of building industrialization and equipment lightweight, the requirements for the adaptability and reliability of fasteners will be further improved. The three-piece fish scale expansion screw, with its unique technical advantages, is expected to achieve application breakthroughs in more fields, providing safer and more stable fastening guarantees for industrial production and civil life.
