What does that mean, 2.5 factor?
Safety Factor - If the calculations show it will fail with a load of X, you design it to withstand a load of 2.5X. That’s the “margin of safety.”
Figure out how strong you expect it needs to be, then multiply by 2.5 to take into account the things you weren't expecting.
2.5 factor means you calculate the strength needed based on the materials then multiply by 2.5 for a safety factor.