Pacific Stair Corporation's 400 Series is designed to accommodate third-party Precast treads. Similar to our 500 Series: The steel pans are modified to fit the finish tread thickness. The stair is manufactured with a smooth surface and the precast concrete treads are applied by the customer after the stair is installed. Our customers have the freedom to purchase precast treads directly through us for the convenience of an all-in-one package or a la carte from third-party vendors.