Tether Products, Male Expression and Self-gratification Thru Innovation



Determining the Size of Your Urethral Orifice

NOTE: These instructions apply only to hard unyielding disk-style retainers.

Ideally, choosing the right retainer size is a matter of finding the largest size that you can comfortably insert thru the constriction of your urethral orifice. The precision this requires to do well may astound you. At the optimum size, a variation of just one French size unit either way (equivalent to a difference in diameter of just one third of a millimeter or little more than one hundredth of an inch) can mean the difference between a retainer that inserts easily and fits perfectly and one that is either quite noticeably smaller than necessary or flat-out too big to go in comfortably. So, unless you are willing to gamble on approximations, measurement needs to be very accurate and precise.

There are basically two ways you can measure your urethral orifice and select the retainer size that best fits you. You can:

  1. Buy one of Tether Products’ unique sizing sounds & dilators (look in the Accessories section), which will not only let you determine the size of your orifice with unparalleled accuracy, but also let you very pleasurably loosen it up and condition it (like a warm-up tool) prior to inserting tight-fitting retainers and, if you want, permanently enlarge it in small controllable stepped increments (unlike no other sound can), or
  2. Simply try different household items until you find something that you think is just the right fit (easier said than done because fit is so sensitive to miniscule variations in diameter) and then determine its French size. If you use the typical sounds sold by other websites, you should not trust their size markings and still measure them, because their size can be off by as much as one French unit, sometimes even more.


Tether Products’ disk-style retainers and sizing sounds conform to the French sizing convention. This convention is used in the medical field to express the size of objects in relation to the size of the incisions or bodily openings that they can pass through and is by arbitrary definition 3 times the equivalent diameter (in millimeters) of the object. Its usefulness lies in the fact that neither the object nor the incision or opening actually needs to be round. The measure can be applied to any x-sectional shape, notably including slits (like your orifice) and oval shapes like those of toothbrush handles, silverware and other household utensils, or irregular shapes that have surface depressions or troughs that body tissues would naturally span.

If you are successful in finding an object that fits just right, its French size can be determined quite easily and accurately by simply measuring the outside girth or least perimeter that a string wrapped tightly around the object would trace. The object doesn’t have to be perfectly round or symmetrical and you don’t need an expensive micrometer or caliper to do it. Here is one simple way.

  1. Tightly wrap a piece of clear or translucent unstretchable mylar tape (the kind used in offices) around the object, enough to generously overlap. If applied crooked or if the object is tapered, the edges of the tape will not align where they overlap. Don’t worry about this; it makes absolutely no difference. But make sure that the tape tautly spans any troughs or depressions on the object.
  2. Use a sharp pin or the point of a razor knife to pierce both layers of tape to create a visible mark at the point on the object where you want to measure and where the tape overlaps. If you are using a tapered object like a pen, the difficulty will lie in determining the point on the object that you think coincides with the narrowest part of your orifice. The more gradually tapered the object is, the more accurate you’ll be.
  3. Peel off the tape and spread it on a clean flat surface.
  4. Measure in millimeters (mm) between the two marks left by the pin or knife and divide that dimension by the number 3.142 (pi) to obtain the equivalent diameter expressed in millimeters at the point on the object where you made the mark. Use a magnifying glass for accuracy and measure the length down to a fraction of a millimeter.
  5. Multiply this equivalent diameter in millimeters by the whole number 3 to obtain the French size.


This technique can be used to accurately obtain the equivalent diameter and French size of any object using only a ruler or tape measure and is as accurate as using a precision micrometer or caliper. Often it is the only way, because few things are ever perfectly round, although they may appear to be.

NOTE: Tether Products’ retainers are designed to just barely slip through edgewise and then later bump up flat against the natural constriction that occurs slightly inside the glans where the internal ligaments and fibers of the penis come together to form a tough ring around the urethra at the top of the fossa navicularis. This critical constriction may not always be evident. In some cases, particularly among circumcised men, the meatus, i.e. the superficial peehole itself, may be even smaller and may obscure this internal constriction. That is, it may be that the urethral orifice has two closely spaced constrictions with the outer one being the smaller. If this is the case then it will be necessary to permanently stretch and enlarge the meatus, i.e. the superficial urethral opening, before a retainer can be properly fitted to slip through and then engage the tough constriction that lies further inside. With no easy way to differentiate the two, the difficulty will lie in determining at what point the meatus is no longer the smaller and influencing size selection. Please pay careful attention to what you are measuring and act accordingly. Enlarging the meatus in such cases, because it is just composed of skin and soft tissue, should theoretically not be difficult, but TP can’t promise anything.

Choosing the Right Size of Disk-style Retainer

Technically, the closer the retainer is to the maximum size of your orifice, the better it will be at comfortably resisting strong tension (if that matters). But the recommended size of a hard unyielding retainer like the stainless steel Model SSR-6 is one that you know will slip in or out with minimal resistance or distension. A retainer that is one or two French sizes less than the absolute maximum size of your orifice (easily determined if you use one of Tether Products’ unique sizing sounds & dilators) is usually best.

There is good reason for not selecting the largest size possible. If your penis is not accustomed to wearing a tetherspout, even if you routinely inserted sounds or probes in the past, you may find that initially some swelling of the urethral orifice occurs with extended wear and that a retainer which was easy to insert later becomes difficult to remove. The swelling won’t be apparent until you try to remove it. If you are a novice it is therefore not a good idea to select a retainer size that will challenge your orifice’s capacity to accept it unless you are willing to put up with the temporary problems that swelling might create. You might have to spend some time to very slowly (and perhaps painfully) squeeze or pull it back out, or be stuck wearing the tetherspout until the swelling naturally subsides. This is usually just a minor temporary hazard that diminishes with time and is really only an annoyance, but one that should nevertheless be taken into consideration.

So take my advice and don’t select too large a size, or do like I do and have several sizes available to choose from. Personally, I no longer experience any swelling and can, when I want, use a size 31Fr retainer very comfortably and conveniently. If I use a sizing sound & dilator to gently stretch and warm it up first, I can even slowly push-in or squeeze-out a size 32Fr retainer (the max my penis will take) with no discomfort and without too much trouble. But I usually select a size 30Fr retainer just as a precaution in case my play gets rough and because it is the fastest to slip in and out (almost no resistance whatsoever). What I find most remarkable is that, despite incessant play and occasionally stretching it almost to the breaking point with things like sizing sounds & dilators, the size of my urethral orifice has not changed in over twenty years. It still amazes me that living tissue can remain so unchanging and be so precisely measurable.