Rebar mechanical splicing systems rely heavily on precision thread geometry to ensure secure and consistent bar-to-bar connections. Among the key parameters influencing connection performance, the thread angle—commonly 60° or 75°—plays a critical role in determining load transfer, manufacturing complexity, and interchangeability.

While most international rebar coupler systems, such as those following ISO, ASTM, or BS standards, adopt a 60° thread angle, Chinese domestic manufacturers predominantly use 75° thread angles. This distinction is not merely a matter of convention but reflects deeper considerations in engineering practice, equipment design, and cost optimization within China’s construction market.

1. Technical Background: Understanding Thread Angle

The thread angle refers to the included angle between the flanks of the thread.

• A 60° thread (used in metric and UNC/UNF threads) has a relatively narrow profile that provides good self-centering and high thread engagement accuracy.

• A 75° thread has a wider thread form, with thicker thread crests and roots, designed to increase contact area and enhance plastic deformation resistance in certain applications like rebar connections.

In rebar coupler systems, the thread must withstand high axial tension and compression, not just rotational torque. Thus, thread geometry affects both mechanical performance and manufacturability.

2. Why China Adopted the 75° Thread Angle

2.1. Manufacturing Simplification

Early Chinese rebar coupler production focused on cold-rolling and cold-forging processes with limited precision tooling.
A 75° thread form allows:

• Easier tool manufacturing and maintenance, as the flanks are less sharp.

• Greater tolerance for rebar diameter deviation, common in locally produced rebars.

• Faster threading speed, reducing tool wear and increasing throughput.This made the 75° system more cost-effective and adaptable to local rebar quality variations.

2.2. Structural Safety Margin

Due to wider flanks and deeper roots, a 75° thread can:

• Provide better mechanical grip under high compressive loads.

• Reduce the risk of thread stripping during extrusion or torque-tightening.

• Maintain reliable performance even with slight misalignment or deformation.

This robustness was valuable during the rapid infrastructure expansion era in China, where field conditions varied and quality control was still developing.

2.3. Domestic Standardization (JG/T 163-2013)

China formalized its 75° thread angle through the JG/T 163-2013 “Rebar Coupler for Mechanical Splicing” standard.
This ensured consistency across domestic manufacturers but created a technical barrier to international interchangeability, since ISO 15835 specifies a 60° angle.

3. International Practice: The 60° Thread Angle

Globally, countries such as the United States, UK, Japan, and most of Europe follow 60° thread profiles, aligning with ISO Metric (M) and Unified National (UN) systems.
Advantages include:

• Global interoperability between couplers and threading machines.

• Higher machining precision with established CNC tool libraries.

• Compatibility with automatic inspection and measurement systems.

However, the 60° profile demands stricter control of rebar tolerances and higher machining accuracy, leading to slightly higher production costs compared with the 75° domestic Chinese version.

4. Cost Comparison

In short, the 75° system minimizes domestic production costs and increases manufacturing efficiency, while the 60° system supports international standardization and higher export compatibility.