This year's chastity experiments have taught me a lot about fit. This is one of those frustrating topics because of the cost of devices and uncertainty about comfort for long-term wear. You'll hear a lot of people talk about fit and issues, but very rarely are things described well enough to figure out what is going on. One-size fits most is only a good thing if you fall into "most" and especially frustrating if you aren't sure the appropriate response, e.g. spending $60 on an additional base ring but not knowing if going smaller or larger will yield more benefit.
I wanted to share a bit that I have learned through extensive and repeated failures with devices that others might find helpful. The topic in particular is about the "burning" feeling that some people develop with certain devices. I have found there are approximately five reasons that lead to the feeling of scrotal burning from a device. This feeling is very non-descriptive and deceptive since it might be caused by more than one reason. Eliminating them one by one should help.
1. Lack of Lubrication
This probably seems rather obvious, but how and where the friction is coming from isn't always obvious. For your choice of lubrication I strongly recommend something long lasting. Silicon-based lube and certain types of butters and oils tend to do rather well. Lotion and water-based lubes will evaporate too quickly.
In my own case I have found that I need to lubricate the inside of the ring all the way around and the front of the ring anywhere it will contact the scrotum. I also lube the inside of the cage, especially along the top where you will come into contact with it when you attempt an erection. In addition to that I lube the underside of the cage on the outside. Depending upon how your anatomy is you may get a significant amount of rubbing/bunching there.
Ideally your skin will glide. If it doesn't, the burn is likely caused by improper lubrication.
2. Skin Stretching
If you have a high and tight scrotum and are using a trapped ball device, there is a very good chance you will get some skin stretching. This can range from mild to painful but its affects can be minimized, however there isn't a set way to do that. Using lotion, butters , or oils on the scrotum will make this less unpleasant. The same things that women use for stomach stretching when pregnant will work on your scrotum.
Ring size can be a major factor but it depends heavily on the design of the device and your anatomy. With some devices, a larger ring will increase scrotal stretching by forcing it to bend out and around the ring. With other devices, a smaller ring will increase stretching by decreasing the space between the cage and the ring, increasing the pull because it happens in a different spot. A lot of this depends on how much space there is between the cage and ring when working from a starting size. Generally speaking, increasing the gap will reduce stretching.
This is very true for devices that have adjustable spacers (e.g. CB-6000). A wider spacer will reduce stretching.
3. Skin Bunching
This is somewhat linked to lubrication but there are other factors involved. Improper ring-sizing and spacing can also cause the skin to bunch in certain spots and cause additional unpleasant friction that can lead to a burning feeling over time.
Making sure that you find an equilibrium with how much scrotum you pull through the ring before attaching the cage can help. This is also the reason that I lube the underside of the cage. Anything you can do to increase the space between the cage and the ring will often help.
4. Excess Hair
Many devices will encourage shaving. Good luck trying to get a CB-6000 on without shaving first unless you really enjoy the feeling of hairs being ripped out. This one gets deceptive because sometimes you might miss a few hairs in an awkward spot and while you might think, "it's only 3 hairs, no big deal," it can become a huge discomfort if they are near a contact point with the ring or cage. If those hairs happen to get laid flat and trapped beneath a contact point, the constant slight tug that isn't enough to rip them out can give a burning feeling that is tough to differentiate from the others.
5. Pinching of Nerves/Circulation
Generally speaking, it's usually quite obvious within a minute or two if you managed to obstruct blood flow or have nerve irritation. However, it is possible to have a fine fit in a flaccid state that is too tight when you attempt an erection.
This is the most deceptive of all types of burns because you will feel fine until you experience intense attempted arousal or frequently linger in a slightly aroused state. In these cases, the swollen state causes a pinched nerve or series of blood vessels that were originally fine and causes nerve irritation. What makes this hard to spot is that the pain will generally be in a different spot from where the pinching is happening. E.g. it will be due to excessive contact on the left side of the penis but the burn will be on the scrotal skin.
Going larger on the ring or wider on the spacing is advisable. In some cases the tube diameter might just be too small.
Hopefully at least one person will find this helpful. The majority of my device failures have been caused by more than one factor at a time, which made it increasingly difficult to figure out the problems. This is a tender area we are dealing with.