【2026 Mechanical Parts】Differences between single-headed bolts and double-headed bolts and their practical applications

I. Appearance: The shank of the single-bolt type has threads on one end, while the other end features a fixed hex head; fixing it is achieved by installing a nut on just one side. The studs of double-headed bolts are divided into half-threaded studs and full-threaded studs; double-headed bolts have threads on both ends and no fixed head, requiring nuts at both ends to be secured.

II. Manufacturing Process The manufacturing processes for single-head bolts and double-head bolts are essentially the same; both fall under the category of fastener production. The main steps include material selection, shaping, thread processing, and surface treatment.

This post was last edited by The one on 2026-6-9 15:52. III. **Application requirements for different types of bolts in accordance with standards and specifications 1) ‘Specifications for the selection of steel pipe flanges, gaskets, and fasteners – Part 1: PN series’ (GB/T43079.1-2023) 6.2.3 Hex head bolts are suitable for applications where the nominal pressure is less than or equal to PN16, the medium is non-toxic and non-flammable, there is no severe cyclic loading, and non-metallic flat gaskets are used. 6.2.4 Equal-length double-headed studs are suitable for nominal pressures of less than or equal to PN40, with non-toxic and non-flammable media, under conditions of no severe cycling. 6.2.5 Fully threaded studs are suitable for all nominal pressure classes, media, operating conditions, and gasket types. 6.2.6 Type 1 nuts are suitable for use with hex head bolts as well as equal-length double-ended studs. 6.2.7 The nuts used in conjunction with fully threaded studs shall be type 2 nuts designed specifically for pipe flanges. 6.2.8 Fasteners shall meet the sealing requirements of flange joints under pre-tensioning and operating conditions.

This post was last edited by The one on 2026-6-9 at 15:53. 2) \"Specifications for the Selection of Steel Pipe Flanges, Gaskets, and Fasteners – Part 2: Class Series\" GBT43079.2-2023): 6.2.3: Hex head bolts are suitable only for applications with a nominal pressure of less than or equal to Class300, where the medium is non-toxic, non-flammable, not subject to severe cycling conditions, and non-metallic flat gaskets are used. 6.2.4 Type 1 nuts are suitable only for applications with a nominal pressure of less than or equal to Class 300, and are used in conjunction with hex head bolts. 6.2.5 Fully threaded studs are suitable for all nominal pressure classes, media, operating conditions, and gasket types. 6.2.6 The nuts used in conjunction with fully threaded studs shall be type 2 nuts designed specifically for pipe flanges.

IV. Practical Significance in Different Application Scenarios 1) Stress Characteristics: During use, bolts are primarily subjected to tensile force, shear force, and torsional force. (1) Single-headed bolt tension: When a tensile force is applied to the outside of the bolt’s threads, the single-headed bolt is primarily subjected to stress on its shank, while the nut serves only as a connecting element. Shear force: The shear force on a single-headed bolt is primarily distributed in the cylindrical portion of the bolt. Torque: The torque on a single-head bolt is primarily generated in the shank, while the nut generally does not experience torque.

(2) Double-headed bolt tension: When alternating tensions are applied to both sides of the bolt, the stress on the double-headed bolt is primarily distributed among the two nuts, the two threads, and the connecting plate. Shear force: When subjected to shear force, the entire double-headed bolt bears the load, and the nuts on both sides share this force, which means its shear strength is greater than that of a single-headed bolt. Torque: When a bolt is subjected to torque, torsional force is generated at the bolt itself, while the nuts on both sides prevent the bolt from rotating.

Considering the combined stress distribution and effects, double-headed bolts of the same specifications have higher strength compared to single-headed bolts.

This post was last edited by The one on 2026-6-9 15:53. 2) Operations and applications (1) Single-head bolts: If the nut on one end becomes rusted, it will make it impossible to remove the bolt. In such cases, methods such as striking or cutting are usually employed to break the studs and nuts in order to achieve disassembly. Without considering pressure levels and strength requirements, if single-headed bolts are used to connect the flanges of equipment and facilities that store or transport flammable and explosive materials, it is very likely that the nuts will rust, forcing the use of methods such as hammering or cutting to remove them. The sparks and high temperatures generated in this process can serve as ignition sources, leading to fire and explosion accidents. If one nut of a double-headed bolt is rusted shut, the other nut can be removed to avoid dangerous procedures such as cutting.

(2) During equipment installation, renovation, and maintenance in chemical and petrochemical enterprises, it is necessary to design and construct various connection fasteners in accordance with regulatory requirements, and select and install bolts as specified by these standards, thereby reducing the likelihood of various leakage incidents caused by improper bolt connections from the outset.

For reference: Some common surface treatment methods—such as electro-galvanizing—can easily introduce hydrogen during the processing stage. For ordinary fasteners, this may not be a major issue, but for high-strength bolts, such risks must be avoided as much as possible in engineering.