Mason Bogie locomotive

The Wm. Mason, an 1874 0-6-6 Mason Bogie and the first locomotive with Walschaerts valve gear built in the United States. Note the intricate decorative work.
Boston, Revere Beach & Lynn #6, an 1886 product of Mason Machine Works. This is a 2-4-4 Mason Bogie. Note the deep firebox permitted by this configuration, and the high reversing shaft (below the bell) with a long lifting link to the valve gear radius rod.
2-4-4T Mason Bogie #10. Mason Machine Works, Taunton, MA. Built 1887. Photo location: Behind the Lynn, MA Train Station of the Boston, Revere Beach and Lynn Railroad. Photo Source: Lynn Museum.

Mason Bogie locomotives (also known as Mason Fairlie locomotives) are a type of articulated tank locomotive suited for sharp curves and uneven track, once commonly used on narrow-gauge railways in the United States. The design is a development of the Single Fairlie locomotive.