help how to fix letters with rods

Is your question in English?

If you are asking how you pad mount letters to a wall, the answer is adhesive.

 

The location in their profile is Mexico, so I'm guessing english is a second language.

To answer the OP's question, Gemini has instructions on mounting on their website https://www.geminisignproducts.com/...0/install-instructions-stud-flatcut-metal.pdf

 

If you are putting up letters like Gemini letters in plasterboard drywall walls, and are going to use just studs, not pads, you just drill holes that are slightly smaller than your studs, with your paper pattern, and then press the letters into the holes. They stay by friction fit. When we do it in harder wall materials like concrete, we drill the holes slightly larger, and put silicone in the hole before inserting the letter.

If you are mounting letters on a wall of hard plastic or maybe wood, or Dibond, I'd suggest using the combination stud/pad, where you drill a hole and the stud acts as a locater for the letter, but adhesive on the pad keeps it from falling out of the wall.

 

I get them from Gemini.