device of that circle area (anal)

there are two areas which you might be referring to, the anus and the sphincta muscle. That hole on your pictures look like they are there for you to poo through, so I would imagine that it doesnt really matter, it would be its position that is more important. I have never measured up for one of those. I would imagine that the hole and its postion are quite generic

 

It's called a hole and they're usually at the rear. I would assume a tape measure could be what is required for the measurement. As for it's comfort, I wouldn't know.

 

Well not easy as a hole is often round but as this is oval so maybe an opening is more applicable. Though holes in the road are often anything but round so it is confusing.

Are we being asked to measure the hole in the device I wonder or the hole in
the op's bottom or the dimensions to place the hole or opening in the device or the identify the location of the op's bum hole which is probably round thus by definition a hole unless he is into fisting in which case its called a rose bud .

The photographs are very nice but provide the reader with evidence that the single steel wire adopted by at least a couple of belt manufacturers may be the best solution in both long term comfort ease of use ie not having to position ones bottom correctly over the hole or opening for a neat evacuation .
The single wire design obviously eliminates the complication of the whole size and placement of holes or openings.

Xx Wendy

 

Oh wendy, please please stop, my sides are literally aching.

 

Dear Mistress B
I try to make the world a happier place.

Xx Wendy

 

Isn't that something the manufacturer of your chosen belt would be able to inform you about? Though my understanding is that for most of them, it's one size fits all.