difference between hilti 5.8 vs 8.8 grade

Hi Mr. Patil, Thanks for asking the question.
The first digit of the grade relates to the ultimate tensile strength of the material (steel) and the second is the ratio of yield stress to ultimate stress, which means, 5.8 grade steel has an Ultimate Tensile Strength of 500 N/mm2 and the yield stress is 80% of the ultimate strength (500 x 0.8 = 400 N/mm2).
Similarly, 8.8 grade steel has an Ultimate Tensile Strength of 800 N/mm2 and Yield Stress as 640 N/mm2.
In case, you wish to check the influence of selecting different grades on your anchor connection, you may raise the design request at : Anchor Design Services - Hilti India
If you wish to learn more about Post Installed Anchoring, please download the fastening book at: E-Books - Hilti India