The metal keyboard with Braille keyboard has a bump in the number "5", which is based on the "Blair Braille principle".

Metal keyboard

Interpretation: Braille, or Braille and Braille, is a text designed for the blind and perceived by touch. It is composed of different combinations of bumps made on the paper through Braille board, braille machine and Braille Printer. Generally, the Braille of each square is composed of six dots. It was created by the blind French Louis Blair in 1824, so it is commonly known internationally as "Blair" in Braille. This is the reason why there is a bump on the metal keyboard keys.