I am doing some custom work to my bike and want to add some passing lights like those on the Limited and road king. I have been searching for housings but keep finding verious sizes 3.5", 4" and 4.5" are most common. Can someone clearify the actual size I should be looking for?

Thanks.

 

My Ultra uses 4.5" blubs in the OEM housings.

 

Stock ones are indeed 4.5", but for a custom look smaller ones would be fine!