20mm x 20mmx 7mm 8 Ohm Mini Cube Speaker..  
Superior Miniature Mini Cube Speaker.
These Speakers are 8Ohms so if are two used then wire in Parallel.
Ideal speaker for many application for use in Bachmann Classes 24 & 25 (Old Model) and the later
Classes 37 & 40, 42, 43, 44, 45, 46, 47, 57, 66, 70, 85.