 The boiler pitch of the Cape 10th Class was at .In the designs of the two Cape 9th Class Mikado types, later the Classes Experimental 4 and Experimental 5, Beatty had achieved improved steaming efficiency by extending the locomotive frames with a bridle casting, such as the one he had designed for the CGR 6th Class 2-6-4 in 1901, to accommodate deep and wide fireboxes.With the 10th Class, on the other hand, he obtained a wide firebox by spreading the grate over the rear coupled wheels, hence the requirement to raise the boiler pitch.