What Is the Strength of L9 Bolts?


L9 bolts -- designed for work environments with extreme stresses and strains -- have ratings in four areas, including tensile strength, proof load, yield strength and hardness. These values vary depending on the bolt's diameter and number of threads per inch.

Tensile Strength

  • Tensile strength refers to the pulling force required to break a bolt. An L9 bolt with a quarter-inch diameter and 20 threads per inch, or a ¼-20, has a tensile strength of 5,720 lbs. A 1-inch, eight-thread L9 bolt has a tensile strength of 109,080 lbs.

Proof Load

  • The proof load means the force required to deform or strip the threads. A ¼-20 L9 bolt has a proof load of 4,610 lbs., while a 1-inch, eight-thread bolt has a proof load of 87,870 lbs.

Yield Strength

  • Yield strength refers to the force required to permanently deform, without breaking, the bolt. The yield strength of an L9 bolt equals approximately 86 percent of its tensile strength.


  • A Rockwell hardness value indicates the brittleness of the bolt. L9 bolts are heat-treated to a Rockwell hardness of R/C 38-42.

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