These are Rectify Series drop-in speaker systems for Kato SD80/90MAc locomotives. There is a front-mount system and a rear-mount system. Choose one or the other or both for maximum impact! The rear system will provide a bigger, deeper sound, but all of the sound will come from the rear of the locomotive. If only using one speaker, you'll need to decide if you want the bigger sound from the rear or less-fuller sound from the front but with better sound-localization.
 
The speakers use a touch of adhesive to mount to the frame. They feature integral rings to route the truck-wires through, keeping them clear of the drive-shaft. The design leaves plenty of room in the middle to mount any kind of decoder and/or motherboard you wish. You will need to discard the factory light-pipes that run to the central PCB and glue LEDs directly behind the lenses - something that should be done anyway.
 
The speakers come fully assembled and tested.
 
Front-mount dimensions are: 12mmH x 18mmW x 39mmL
Rear-mount dimensions are: 17mmH x 14mmW x 71mmL