The qualified standards for the rebar coupler are as follows:

1. The rebar coupler is made of 45 high-quality carbon structural steel with reasonable design, advanced technology, high dimensional accuracy, and reliable connection quality.

2. The basic parameters of rebar couplers are designed in accordance with the strength requirements of HRB500 steel bars, and also can be applied to HRB335 and HRB400 rebars.

3. The performance indexes of the rebar coupler have been tested by the "National Construction Engineering Quality Supervision and Inspection Center", and all of them meet the requirements of the "I" class joint in JGJ107-2016 Technical Regulations on Mechanical Connection of Rebar.

4. The specifications match the diameter of the connected steel bar, being divided into ten regular specifications: φ14mm, φ16mm, φ18mm, φ20mm, φ22mm, φ25mm, φ28mm, φ32mm, φ36mm, φ40mm, as well as special specifications: φ10mm, φ50mm.

5. Three series (standard rebar coupler, left-handed and right-handed rebar coupler, and reducer rebar coupler) and 52 varieties can meet the requirements of the same diameter, reduced diameter, and adjustable length and direction of the connecting steel bar in the transverse, vertical and oblique parts of the building structure.