This is a good speaker for most steam applications but be sure to check the decoder instructions first. some decoders like the SOUNDTRAXX PNP that replace the light board and some others require a speaker with 1-2 watts power and these speakers will not function with those decoders. I have used many of these and have had good results.
Very common sized round speaker. Easily fits many locos. Some Katousa models come with the enclosure built in. The wiring harnes plugs into the Soundtraxx board. I have many locos with this speaker. Always at a good price on ebay.