The Rhymney Railway M class was a class of 0-6-2T tank locomotive introduced into traffic on the Rhymney Railway in 1904. These were substantial sized tank engines, and weighed 66 long tons and were 36 feet 9 inches (11.20 m) in length.

The Rhymney Railway A class were 0-6-2T tank locomotives introduced into traffic in 1910 and designed by the railway's engineer Hurry Riches. These were substantial sized tank engines, and weighed 64 long tons and were 35 ft 9 in (10.90 m) in length.