Collett further developed the 4-6-0 type as the ideal GWR express locomotive, extending the Stars into Castles in 1923, and then producing the largest of them all, the four-cylinder King class, in 1927. He also produced slightly smaller types for mixed traffic (either passenger and goods) duties, the Hall class in 1928, the Grange class in 1934, and the Manor class in 1934. All these continued to carry appropriate names. For lighter goods services he produced his own standard 0-6-0, the 2251 class.