8.8 double-ended bolts are high-strength fasteners with threads at both ends and no bolt head, enabling bidirectional fastening. They are suitable for applications where standard bolts cannot be inserted, where space is limited, or where a high-strength seal is required. The designation ‘8.8’ represents the performance grade; the first digit, ‘8’, indicates that the minimum nominal tensile strength of the finished bolt is 800 MPa; the second digit after the decimal point, “8”, indicates that the ratio of the bolt’s yield strength to its tensile strength (the yield-to-tensile strength ratio) is 0.8; based on this, the nominal yield strength of an 8.8-grade double-ended bolt is calculated to be ≥640 MPa.
Grade 8.8 double-ended bolts are typically manufactured from 45 steel (medium-carbon steel) or certain medium-carbon alloy steels. They must undergo quenching and high-temperature tempering heat treatment to meet the required mechanical properties. This distinguishes them significantly from Grade 4.8 low-carbon standard bolts, which are produced by cold heading without heat treatment, in terms of material, manufacturing process and load-bearing capacity.
Grade 8.8 fasteners are classified as medium-to-high-strength fasteners, offering excellent tensile and fatigue resistance. They are widely used in medium-load applications such as flanged pipe connections, automotive chassis assembly, general machinery frames, small and medium-sized pressure vessels, and steel structure fastening, making them one of the most commonly used types of double-ended studs in industrial installations.

• High-strength connection: Suitable for heavy-load and vibration-prone applications, far exceeding the performance of standard Grade 4.8 bolts.
• Double-sided clamping: Ensures even load distribution and excellent sealing performance, ideal for flange and pressure vessel connections.
• Space-saving design: Headless design, suitable for confined spaces or enclosed structures.
• Reusable: Easy to dismantle; repeated assembly and disassembly does not affect core performance.
• Excellent value for money: Industrial ‘general-purpose’ high-strength bolts, balancing strength and cost.

Pre-tighten one end into the threaded hole in the base (the double-nut method may be used for securing)
Fit a nut onto the other end and tighten in a symmetrical criss-cross pattern in 2–3 stages to the specified torque
We recommend using a torque wrench to ensure uniform preload
Apply a lubricant such as molybdenum disulphide to the threads to reduce the coefficient of friction