Getting a proper fit is necessary for any regular wear of a chastity device. Mature Metal builds the device to your specs. It's a little tricky to measure, but as long as you get the cage right adjustments of the base ring are inexpensive. Expect to get a couple of adustments.

I recommend using something like A&D ointment on the penis when going into the cage as well as a little dab where the bottom of the base ring rests under the scrotum. This avoids the little pinches that make chastity unnecessarily uncomfortable.

If you're worried about falling out of the device, Mature Metal offers an "anti-pullout" pin on some models. Also, go for the smallest gap between the cage and base ring -- it might be tight in the beginning, but you'll get used to it and your balls won't slip through.