Steel does ×2 to Fairy

Generations VI to IX, single types. The other way round, Fairy against Steel, is ×½.

65 Steel and 64 Fairy species among the 1025 this site covers.

Attacker, Grass and Steel Kartana sprite

Kartana #0798

damage×2Generations VI to IX

Defender, Fairy Florges sprite

Florges #0671

Steel and Fairy did not exist in Generation I and Generations II to V, so Steel against Fairy has no value there.

Strongest Steel attackers

Kartana leads Steel at Atk 181

Sturdiest Fairy defenders

Dual types that change the answer