I think using the search feature would yield the answers you crave... Answer/ length up to a point... then the thicker the better but again, up to a point. Over 7 around is a challenge, thankfully im only 6-1/2 around (IMHO, perfect) but I would be willing to give up an inch just to slam it home all the time! Im 9-3/4 long and can count on my hands, how many times Ive buried it balls deep.