The smallest that I can recall was when I was still in High school. This black guy and I hooked up somehow, probably the old phone lines, and he came up to see me, we rented a motel room etc. I just remember his dick being so skinny that I reminded me of a pencil. I didn't even feel it when he was fucking me and I hadn't been fucked that much at this point.
The biggest I ever had is a toss up. There was a 9 inch that was average thickness attached to a guy who really didn't know how to use it as a top. But it was an okay fuck non the less and this was back in the late 90's. The other one was about 8 or so long and was beer can thick at least. This one I remember because he broke a long dry spell and I think he may be the one who pozed me.