3/4 inch if it will fit. It will be something that has to be built. Not very hard just a circle with the cutout for the speaker in it. MAke sure not to use dry wall screws when you put it in. For best results put some silicone "I prefer window silicone black. They have some at home depot that doesnt stink up your car for a month" on the backside of the mdf ring to seal it to the door.