Most accurate way to measure diameter?

[chaste4fun]

I measured several times and took averages of each measurement before buying my MM jailbird. Somehow everything came out perfectly, except the internal diameter; the one dimension that can't be adjusted. It's too big and allows for too much growth which can be uncomfortable (and not in a good way). Additionally it allows the whole device to ride down a bit when I'm flaccid which makes it near impossible to wear through the night.

So what's the most accurate way to measure the diameter you'll need? I just tried by using some string to get the circumference of my flaccid shaft and finding the diameter from that but the result was actually 1/8" bigger than my current ID. :/ I'm going to buy a new device but I need to be sure I have the correct diameter this time.

[Shepherdsflock]

If you can get your hands on a set of vernier or dial calipers, that would get the job done. Otherwise, you could try a pi tape. Or, I have a laser tracker I could sell you for $85,000. Measure your manhood with an accuracy of 10 microns.

[chaste4fun]

If you can get your hands on a set of vernier or dial calipers, that would get the job done. Otherwise, you could try a pi tape. Or, I have a laser tracker I could sell you for $85,000. Measure your manhood with an accuracy of 10 microns.

I would take the laser tracker, but I was really hoping to measure within 10 nano meters. :/

I don't have calipers (though I've been meaning to buy some) but I do have a vice. I suppose I could close that until it makes contact and measure the gap. Thanks for the idea!

Funny, I was really convinced I'd never be voluntarily putting my penis in a vice. What a strange world we live in.

[Shepherdsflock]

Funny, I was really convinced I'd never be voluntarily putting my penis in a vice. What a strange world we live in.

I never in a million years would have guessed that I would voluntarily lock my penis in chastity device. You just never know what you'll do out of necessity (or desire).

[ManagedMan]

Once you have an idea for the internal diameter, buy a metal or rubber ring of that diameter. Take the ring and pass it over your penis during different periods of the day to see how easily it goes over, or not. I used this technique to validate whether a slightly larger ring was right for my Contender. It ended up being perfect.

[Tom Allen]

The only thing I would add is that your penis is not perfect cylinder; that is, you could use a calipers and measure across north/south, and come up with a different number east/west. It will, however, expand to *fit* a cylinder if the space is small enough.

I'm not sure why measuring the circumference and dividing by 3.14 didn't work, but certainly trying rubber O rings of various sizes would be an acceptable alternative.

[chaste4fun]

The only thing I would add is that your penis is not perfect cylinder; that is, you could use a calipers and measure across north/south, and come up with a different number east/west. It will, however, expand to *fit* a cylinder if the space is small enough.

I'm not sure why measuring the circumference and dividing by 3.14 didn't work, but certainly trying rubber O rings of various sizes would be an acceptable alternative.

Yeah I'm sure it's just error from not picking a great way to measure. At any rate, I bought some washers from Lowe's with the internal diameters I'm thinking about and I'm hoping that'll provide a better way to do this.

Edit/Quick Update: I am very torn between the 1 1/8" and 1 1/4" sizes. The smaller size seems like it'd be too tight and become uncomfortable, while I'm still concerned about the larger being too wide, even though it seems to hug fairly nicely. I wish they had an inbetween size.

[zorglub]

The only thing I would add is that your penis is not perfect cylinder; that is, you could use a calipers and measure across north/south, and come up with a different number east/west. It will, however, expand to *fit* a cylinder if the space is small enough.

I'm not sure why measuring the circumference and dividing by 3.14 didn't work, but certainly trying rubber O rings of various sizes would be an acceptable alternative.

I wondered about that too... Since a cylinder has less volume when it is squished, measuring a perimeter on such a shape and deriving the diameter for a cylinder containing the same penis volume may introduce an error, but how much error would we be talking about ...

*** Geek alert ***
I am not one to pass up such an opportunity to apply math to real-world chastity problems!
I chose two models for a squished penis cross section: an ellipse and another form of "flattened circle": a figure composed of a rectangle with a half circle added at each short end, which I dubbed a "flatoid". I then calculated formulas for the ratios between the perimeters of these shapes and the circumference of a circle of same surface.
I then charted the error (overestimation) of the circle circumference as a function of the penis height (north-south thickness) to width (east-west thickness) ratio:

flattened cylinder perimeter ratios.jpg

With, say, a 1" 3/8 inner diameter cage, an error of 1/8" diameter would be 9%. Per the above chart, that kind of error would occurs between 48% and 55% height-to-width ratio.
My personal observation, when standing and holding the penis horizontal by just supporting it underneath, is at worst 80% height-to-width. If I hold it firmly (not painfully though) between index (under) and thumb (above), I can get 65%...

So it seems natural (as opposed to forced) flattening while measuring perimeter with a string does not fully explain an 1/8" error. Oh well

[Tom Allen]

While I enjoyed the geek approach, I had another thought. The not-quite cylindrical shape would apply to a full (or near) erection. But a flaccid penis is probably closer to a cylinder because it has not become blood engorged, meaning that wrapping string or an actual cloth tape measure should be more accurate. After all, the idea is to be in a cage that *prevents* erection, or else it becomes painful.