What are the main differences between machine screw anchors, expansion bolts and sleeve anchors

In the construction and engineering fields, anchoring technology is the cornerstone of structural safety and stability. Machine screw anchors, sleeve anchors, and drop-in anchors are three common and widely used types of mechanical anchors. While all achieve their anchoring effect by generating expansion forces within the base material, they differ significantly in their operating principles, installation methods, applicable base materials, load-bearing performance, and application scenarios. Understanding these differences is crucial for selecting the most appropriate anchoring solution and ensuring project quality.

Operating Principle and Structural Differences
The core of the machine screw anchor lies in its unique internal plug design. It consists of a hollow, internally threaded metal sleeve and a separate tapered metal plug. During installation, the anchor sleeve is placed into a pre-drilled hole. A hammer or specialized installation tool is then used to drive the internal plug into the sleeve, forcing the lower end of the sleeve to expand outward and securely engage the hole wall. This design allows for the screw or threaded rod to be inserted after expansion is complete, hence the name "pre-expansion" anchor. An expansion bolt typically refers to a one-piece expansion bolt with a nut and washer. Its construction consists of a shank, a tapered head, an open expansion sleeve, and an external nut. When the nut is tightened, the shank is pulled, and its tapered head pushes the open sleeve outward, forcing it against the hole wall and generating expansion force. The expansion process of the expansion bolt occurs simultaneously with the tightening of the nut.

Sleeve anchors (also known as hammer sleeve anchors or pre-cast anchors) are similar in design to machine screw anchors, but their expansion mechanism is slightly different. They typically consist of an internally threaded metal sleeve and a tapered expansion cone inside. During installation, the sleeve is fully inserted into the hole, and then a special tool or punch is used to drive the expansion cone downward, causing it to expand inside the sleeve and secure it to the hole wall. Similar to machine screw anchors, these are also "pre-expanded" and are screwed into the threaded rod after expansion is complete.

Installation Method and Convenience
The installation process for machine screw anchors consists of two steps: first, inserting the anchor sleeve and tapping the inner cone to expand it, followed by threading the screw. This step-by-step process ensures a high degree of control over the installation process. If the connection needs to be removed and reinstalled multiple times, machine screw anchors are very convenient because their fixed portion remains stable in the base material, requiring only the screw to be screwed in and out.

Expansion bolts are installed in a single step. Tightening the nut simultaneously expands and secures the bolt, making the process quick. However, this one-piece design means that if disassembly is necessary, the entire expansion bolt must be removed or sheared off, negating the advantage of reusability.

Sleeve anchors are also relatively simple to install. Typically, expansion is achieved by inserting the sleeve into the hole and striking the punch with a hammer. This efficient installation method is particularly suitable for mass installations. Like machine screw anchors, they also support repeated threaded removal and installation.

Applicable Substrates and Load-Bearing Performance
Machine screw anchors, with their unique internal tapered expansion mechanism, provide stable load-bearing in a variety of substrates, particularly excelling in substrates such as concrete, brickwork, and hollow blocks. Their evenly distributed expansion force exerts relatively little stress on the substrate, making them ideal for use near edges or in areas of weaker substrate strength.
Expansion bolts concentrate their expansion force at the tapered head of the bolt shank, generating greater radial expansion force. While they perform well in strong concrete, this concentrated expansion force may cause cracking in brickwork or hollow substrates. When bearing heavy loads, their pullout performance outperforms their shear performance.
Sleeve anchors also perform well in hard concrete. Their expansion mechanism ensures strong pullout force. They are typically used for medium to heavy-duty fixing applications, such as pipe, equipment, and bracket installations.

Application Scenarios and Economic Considerations
Machine screw anchors, due to their reusability and substrate-friendly nature, offer significant advantages in applications requiring frequent maintenance, repair, or disassembly, such as the installation of machinery, pipe supports, and cable trays. Expansion bolts, due to their simple and efficient installation method and strong load-bearing capacity, are widely used in the fixing of building structures, steel structures, and heavy machinery, especially in one-time permanent installations.

Sleeve anchors are commonly used for medium-to-heavy-duty fixings, such as suspended ceilings, air ducts, and fire sprinkler systems. Their embedded installation method allows them to be flush with or below the substrate surface, without affecting subsequent construction.