These iron horseshoes come in a set of four. While all four shoes are affixed to the hooves of a horse, centaur or similar creature, they increase the creature's walking speed by 30 feet.

These are the Centaur version of 'Horseshoes of Speed' so they work correctly, on a Centaur in D&D Beyond GUI. 

Notes: Bonus: Speed (Walking), Centaur, Buff, Movement, Exploration