These are Rectify Series drop-in speaker systems for Kato P42 locomotives. The speakers drop into the factory cavity and use carpet-tape or a dab of adhesive to secure them. No modifications are needed.
 
The speakers come fully assembled and tested.
 
Dimensions are:
Front-mount: 25mmDia x 7mmH
Rear-mount: 25mmDia x 10mmH
 
VIDEO: https://youtu.be/PUom3Vf-XDc