What distance between ball ring and tube

Probably. It’s good that you decided to remove and heal. Health and comfort are primary. Chastity needs to be a safe secure home, not an exercise in temporary CBT! With a snug cozy cage, you’ll find yourself wanting to be kept locked.

To your question... Over time my balls have become accustomed to a narrow 6mm gap and a tighter base ring in my custom Contender cage. Depending on mood, my keyholding wife will put me in a larger more forgiving device. Keep your base ring for the future.**

I was wearing 9.5mm (3/8”) just fine but I wanted a bit less length total, so I stepped down a 1/4”.

10 mm (about 3/8”) is a fairly standard ball gap. I’ve seen 12 mm (about 1/2”) as well. 15 mm seems excessive. That’s very generous for me.

With a larger gap, you need to ensure your balls don’t slip back through your base ring. But that’s a factor of base ring diameter. I’ve been surprised what can slip through. A large base ring and small gap isn’t always enough to trap one’s balls.

Comfort and health is key. A few millimeters (3 mm or ~1/8”) can make a world of difference. Go for an updated fit.

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**Edit: I see the London Tower ball gap is defined by the cage, not the base ring.

But it’s a very similar device to my Contender. An open design made of 316L stainless steel rods. I’m assuming your balls are pressing up against the bottom of the cage ring and it’s pressing into your flesh.

I use a cyclist’s anti chafing creme called Chamois Butt’r. It helps a lot. I also keep trimmed.

 

People here can only give you advise on what cage to purchase or what size of a ring or spacer you require. Everyone is built different and finding the best fit for you takes some testing.

From my experience a cage that is snug so it doesn’t move around much is more comfortable for long term lockup. Shorter than you are flaccid works good for me to reduce pains from nocturnal erections also. No one knows your cock like you do, you’ve been playing with it for years.

 

i am now locked in a MM Jailbird, 3/8 inch gap is what MM finds to be the average, its what i have and is perfect.

 

it's also going to vary based on what size your base ring is. Think of it as a right angle triangle, where the ring to cage gap is the one leg, the horizontal distance from the edge of the cage to the edge of the ring is the other leg, and the true ball gap is the hypotenuse of that triangle. If the diameter of the base ring is larger and the distance for ball ring to cage ring is unchanged, the actual gap gets bigger...

When I'm doing a design for someone, that hypotenuse is typically between 13.5 mm and 17mm.

 

Be careful when quoting the "ring gap", especially translating it from one device to another, as not all 8mm gaps are the same!

To paraphrase what JLJ says:
If you increase the diameter of the penis tube (keeping everything else the same) then the with the same base ring and "gap", the space between the rings will get smaller.
If you increase the diameter of the base ring, then with the same tube and "gap", the space between the rings will get bigger.

To really understand the exact sizing and fit of your device you need to measure the actual distance between the two rings at the bottom, not the parallel separation between them.

 

I should have attached a picture!

here the "gap" is 8.2mm (lower left), but the measurement I adjusted to was the 15.68 (lower right). If the ring were larger, the 8.2 would have needed to be smaller to keep the 15.68 constant.