In the metric system 8 inches is about 20 cm. The significance of the number 20 is quite clear to me. When I had no knowledge, just hearing someone (e.g. in TV) refering to 20 cm was a spine-chiller. It was just something that was used in comedy, and the unwritten consensus was that this was not met by 99%+ of people. Nowadays 25 cm = 10 " still seems to be realistic. But I think this is a biased perception already, because I am so used to this
MOS and �naked people movies� environment. 6 inches girth is equal to 15 cm. Then you have 15 and 20, these are nice numbers I would say. Not sure whether 30 cm cocks exist, but I am quite sure that 40 cm cocks do not exist.