Hexagon head reamer bolt

Hexagon head reamer bolt— Product Introduction

Fit bolts are high-precision fasteners specifically designed to withstand lateral shear loads and provide precise positioning, manufactured in accordance with GB/T 27 (Chinese Standard), DIN 609 (German Standard), and other applicable standards. Their most prominent feature is the precisely machined smooth shank section, with extremely tight fitting tolerances (typically h8 or m6), enabling a close transition fit or minimal clearance fit with the reamed holes of the joined components. These bolts are made from high-strength alloy steel (such as 40Cr, 35CrMo) or premium carbon steel, and after quenching and tempering, achieve high strength grades ranging from 8.8 to 12.9. They are widely used in construction machinery, transmission equipment, and steel structures — applications where key connections must withstand alternating loads and require precise alignment.

I. Product Features

• Precisely machined shank diameter: The non-threaded section (smooth shank) of the bolt has a significantly larger diameter than ordinary bolts and is manufactured to h8/m6 precision, allowing it to fit closely with reamed holes, directly bearing shear forces and preventing lateral misalignment of the joined components.
• Standardized high-tolerance grades: Fully compliant with the dimensional tolerance requirements of GB/T 27 Grade A/B and DIN 609, with strict control of the coaxiality between the smooth shank and the threaded section, ensuring consistency and interchangeability in batch production.
• High-strength material foundation: Typically made from premium alloy structural steel such as 40Cr or 35CrMo, after quenching and tempering, the shank section achieves uniform hardness while maintaining high strength and excellent impact toughness.
• Diverse anti-loosening structures: In addition to the standard smooth-shank type (GB/T 27), variants include bolts with a pin hole at the shank end (GB/T 28) or a hole in the head (GB/T 29), which can be used with cotter pins to effectively prevent the nut from loosening under severe vibration.
• Versatile surface treatments: Depending on operating conditions, treatments such as blackening, zinc plating, nickel plating, phosphating, and bare stainless steel are available, balancing the requirements of rust resistance, wear resistance, and appearance.

II. Product Advantages

• Outstanding shear resistance: The smooth shank section directly contacts the hole wall to bear lateral forces, and its load-bearing capacity far exceeds that of ordinary bolts which rely on preload to indirectly prevent slipping. This fundamentally avoids bolt fracture caused by component slippage.
• Precise positioning, ensuring assembly accuracy: The extremely small clearance between the bolt shank and the hole wall allows it to function as a positioning pin, precisely fixing the relative positions of flanges, gearboxes, connecting rods, and other components, while maintaining original alignment accuracy even after repeated assembly and disassembly.
• Anti-loosening and vibration-resistant, safe and reliable: The tight fit itself prevents micromotion wear between components, which is particularly effective in vibrating environments (such as engine brackets and boom connections). When combined with pin-hole anti-loosening structures, the safety factor is even higher.
• Long fatigue life: Thanks to the precise fit which reduces direct shear on the threads from impact loads, and the high fatigue limit of the heat-treated material, the service life is significantly superior to that of ordinary bolts.
• Simplified assembly process: On-site complex reaming-and-bolt-matching procedures are no longer necessary — simply selecting the appropriate standard fit bolt meets both the shear and positioning requirements of the design.

III. Applications

• Construction and Mining Machinery: Critical connection pin locations such as loader booms, excavator arm links, and bulldozer push arms.
• Lifting and Conveying Equipment: Crane slew bearings, heavy-duty transmission shaft universal joints, and fixation of heavy rollers and chain wheels.
• Power and Transmission Systems: Flywheel-to-crankshaft connections in diesel engines, large-power motor end covers, and positioning and fastening of gearboxes to bases.
• Steel Structures and Bridges: Steel structure nodes, bridge bearings, and tower connection flanges subjected to bidirectional or multi-directional complex stresses.
• Automotive and Rail Vehicles: Critical safety locations such as heavy-truck leaf springs, balanced suspensions, rail vehicle bogies, and traction devices.
• Precision Machine Tools and Dies: Guide and fixation of press slides, injection molding machine platens, and large stamping dies — applications demanding high repeated positioning accuracy.