I took a picture to show you the difference. The housing with the smaller hole is the inboard housing that has the taillight only bulb socket. The larger hole is outboard and fits the bulb socket with the brake light, turn signal and taillight. It seems that the outboard housings are easier to find NOS. It might be possible to use an outboard housing for the inboard bulb socket, but I don’t know. I haven’t tried. Hope this helps.