Straight-line insert of the 27x3.
If you want to go deep, better go wide first, for many good reasons.
Even when I know I just had it inside.
The largest of the three available sizes measures at 39.
This is a dangerous form of masturbation, and I'm not a doctor, but I don't think you could get one to recommend it.
The wall of your rectum is chalk full of blood vessels, and you'll probably end up with some blood if you're too rough with yourself.