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The difference between bolts and self-tapping screws？
In the field of mechanical connections, bolts and self-tapping screws, as two core fasteners, often have their differences overlooked by non-professionals. Bolts are typically composed of a head and a shank and need to be used in conjunction with nuts or pre-threaded holes. Their standardized strength grades (such as 8.8) clearly indicate tensile performance and are suitable for heavy-duty scenarios such as steel structures and Bridges. Self-tapping screws, on the other hand, achieve the function of directly penetrating materials through special thread designs (such as coarse pitch and cutting edge) without the need for pre-drilling. They are commonly used for quick connections of wood, plastic, and thin metal plates. This essential difference leads to a significant distinction in material selection between the two: bolts mostly use medium carbon steel or stainless steel and are treated with galvanization to enhance load-bearing capacity, while self-tapping screws rely more on the plastic deformation capacity of zinc alloys or low-carbon steel.
From the perspective of application scenarios, bolts are mostly used in situations such as automotive chassis and building steel structures where repeated disassembly is required, while self-tapping screws are mainly concentrated in one-time or lightweight connection demands such as furniture assembly and electronic device casings. From the perspective of structural design, the difference between bolts and self-tapping screws is first reflected in the shape of the thread. Bolts with fine pitch standard threads (such as M6×1.0) need to fit with nuts or prefabricated threaded holes, and the thread strength is directly related to the tensile performance. Self-tapping screws, on the other hand, feature a wide pitch and high thread cutting design (such as ST4.2×1.8). They form internal threads by squeezing the material through the acute Angle of the thread edge when screwed in. This self-tapping characteristic enables them to directly penetrate soft materials like plastic and wood. In terms of head structure, bolts are mostly hexagonal or square heads to facilitate operation with a wrench, while self-tapping screws are commonly designed with cross grooves or straight grooves, which are suitable for quick installation with a screwdriver. In terms of material selection, bolts typically use medium carbon steel or stainless steel (for instance, 10.9 grade bolts need to be quenched), while self-tapping screws mostly adopt low-carbon steel or zinc alloy to maintain the toughness of the cutting edge. In addition, the screws of self-tapping screws are often designed as conical or with cutting edges (such as tail-cut self-tapping screws), while the bolts remain cylindrical to match the thread fit of the nuts. These structural differences directly determine the application scenarios of the two: bolts are suitable for the connection of steel structures that need to bear lateral loads, while self-tapping screws are better at the rapid fixation of thin plates and soft materials. In terms of the selection of application scenarios, the difference between bolts and self-tapping screws is like the division of labor between heavy-duty trucks and urban mobility vehicles. Bolts, due to their high strength and disassemblability, have become the preferred choice in fields such as steel structure buildings, bridge engineering, and heavy machinery. For instance, the connection of car chassis needs to withstand severe vibrations. Bolts of grade 8.8 and above, when used in conjunction with anti-loosening nuts, can ensure long-term stability. Self-tapping screws are like precise surgical knives, demonstrating advantages in scenarios such as furniture assembly, electronic device casings, and plastic component connections: their feature of not requiring pre-drilling significantly enhances efficiency. For instance, using ST3.5 self-tapping screws to fix computer motherboards can prevent metal debris from damaging circuits. The selection in special environments shows more differences: Chemical equipment requires stainless steel bolts (such as A2-70) to resist corrosion, while outdoor wooden structures rely on galvanized self-tapping screws to prevent rust. It is worth noting that incorrect mixing may lead to disastrous consequences - a certain car factory once caused the connection parts of the vehicle to break during driving due to the misuse of self-tapping screws to fix the chassis. This scene differentiation essentially stems from design logic: bolts pursue absolute reliability, while self-tapping screws focus on convenience and economy.