Rebar coupler systems, sometimes also known as mechanical splices, are usually used as an alternative to traditional steel bar connections in construction. Rebar couplers can be divided into first-grade steel, second-grade steel, and third-grade steel according to their tensile strength, compressive strength, and other properties. What is the grade classification standard of rebar couplers, and what is the difference between different grades of rebar couplers? 

1. The rebar coupler whose tensile strength is greater than or equal to 1.1 times the ultimate tensile strength of the steel bar is the first-grade rebar coupler. The first-grade rebar coupler has better tensile performance and is suitable for parts requiring higher tensile strength. 

2. A rebar coupler whose tensile strength is greater than or equal to the standard value of the ultimate tensile strength of the steel bar is a second-grade rebar coupler. The tensile performance of the second-grade rebar coupler is moderate, which can meet most of the requirements of steel bar connection.

3. A mechanical splice with tensile strength greater than or equal to 1.35 times the standard yield strength of the steel bar is a three-grade rebar coupler. The three-grade rebar coupler is suitable for the part of concrete structure where the tensile strength requirement is not high, so it is rarely used in actual construction.