A burner throat is defined by a cage of tubes and is lined by fitting refractory tiles. A plurality of retaining means each having two joined parts, the outer part abutting the tubes and the inner part exerting an abutting force radially inwards on the tiles to retain them in position. In use the abutting force on the tiles can be varied to suit the design characteristics and environment, by varying the exposed length of a pin which threadedly mates in a complementary bore in each of the two parts. To further secure the tiles, a dowel is provided to mate in complementary bores formed in an adjacent side of abutting tiles.