Well now, going along with Noey's findings using a vibrator of some dimension (42mm diameter, 7"long) ... and initially not being the least aroused the thing hardly wants to get inside in the first place

Eventually though it will go, and it would be *VERY* painful to force it - before it wants to go.
Call this step one.
Step two, starting to get into it, and I'm speaking here of 1/2 hour quite easily, one wants that thing to REALLY go DEEP, deeper, deepest!
Mother Nature then having HER way I guess?
The difference between the initial (reluctant) and finally (willing) stage is at least 1". Though in my case 4 ½" is the end of the flag pole so to speak – which gets me back to "relevant" depths.
A penis is
thankfully not as firm as a normal vibrator or dilator, yet bumping real harsh into our internal dead-end is PAINFUL. Ouch!

Well, to me it is, and when Dr Sanguan did his check-up shoving a speculum of some proportions up there (size of a barbeque tongues) just 3 weeks back... ouch! Yeak!
It gave me an idea about what it's like to have a pap smear. Not a very nice thing and he did not even take any samples.
At least all had healed very well, was his finding.
4 ½" - relevant depth (aroused)? That is the question – and if ever I find out, I shall share my findings

Axélle