Security Sheet Metal Screws

In addition to the cross-column form, the head drive structure of Security Sheet Metal Screws also widely adopts special-shaped designs such as inner pentagon, inner triangle, and one-way groove. These unconventional groove shapes are incompatible with standard tools and require the use of special bits to apply tightening or disassembly torque. According to DIN 34800 testing requirements for the structural strength of anti-theft fastener heads, the depth and width of the internal pentagonal drive groove must meet the requirement that the deformation of the notch in the breaking torque test is not greater than 0.1 mm. For screws with ST4.8 specifications, the safe tightening torque rating is 2.5 Nm, and the breaking torque is not less than 5.5 Nm according to the ISO 7051 test method. The ratio between the two is approximately 0.45, which provides a sufficient safety margin for the notch. At the same time, there is a guide cone surface at the end of the screw. The cone angle is 25 to 35 degrees according to the ISO 1478 standard, which facilitates automatic centering in the prefabricated hole, reduces the risk of tilted penetration, and provides effective protection in environments with clear requirements for anti-disassembly, such as prison facilities, bank equipment, and subway car interiors.

Under special protection level requirements, anti-theft sheet screws can use solution-treated austenitic stainless steel instead of carbon steel to enhance corrosion resistance and non-magnetic properties. According to ISO 3506-1 regulations for A2-70 grade stainless steel fasteners, the tensile strength is not less than 700 MPa, the axial drilling resistance when penetrating a 2.0 mm thick galvanized steel plate is approximately 320 Newtons based on actual measured data, and the surface passivation film has been verified by ASTM A967 standards to withstand the neutral salt spray test for 480 hours without red rust. In addition, a brittle fracture slot design can be added to the screw head. When non-special tools are used to forcibly twist the screw, the slot will break when the torque exceeds 6.5 Nm, making the screw unable to be screwed out normally. According to the manufacturer's ultimate torque test report, this design has a successful prevention rate of more than 95% in the anti-theft damage test. According to the ISO 9227 Copper Accelerated Acetic Salt Spray Test Method, the stainless steel version remained unchanged in appearance for 720 hours in an acidic salt spray environment, which is sufficient for the installation of outdoor security equipment in coastal cities. Its dual capabilities of anti-corrosion and anti-violent disassembly make it the preferred solution for securing screws for confidential instruments, communication base stations, and public seats.

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