The difference in the strength between Fe-415 and Fe-500 grades is 20%, Fe-500 being 20% stronger than Fe-415. The reason for this is as follows: – Fe-415 denotes that a force of 415 N/sq.mm. is required to deform the TMT bar, whereas Fe-500 denotes that a force of 500 N/sq.mm is required to deform the TMT bar. https://bit.ly/3KV51a1