Anal canal length?

So, I’m curious if the anal canal from the sphincter back until it opens to the rectum has a specific length. When it comes to butt plugs the length of the narrow neck, seems to me, would be important. If it’s too long the fit would be sloppy, if too short the plug may either come out or slip in. The right length would be just long enough so the wider parts of the plug could be felt inside and outside forcing you to keep contracting your anal muscles. Is there a butt plug with an adjustable neck length? Does anyone make custom fit plugs? Also, while I’m at it, are there any plugs to which you could add weights forcing the wearer to constantly clench to avoid the plug being yanked out?

I very much like the idea of an adjustable butt plug

I have never really thought about it much, i have some with long necks and some short .The neck width is what I really remember. My Doc Johnson style ‘Classic’ plugs have a narrow neck and certainly more comfortable to wear out and with the narrow neck there is no danger of slip outs. I have a large plug with a wide neck, its so stimulating in but you couldn't wear it out!!

I would be willing to try anything though.

What I would find ideal would be a steel plug that had interchangeable necks / bases which could be safely and securely attached. I love the plug I'm using now but if I could attach a neck to it that was thinner and a little longer it would be absolutely perfect!

Got me thinking - just what is the anal canal? So I did a search and found this with a good descriptive picture: https://teachmeanatomy.info/abdomen/gi-tract/anal-canal/