We all know how getting the right size is important. The context here is a custom-sized metal CD (metric system ). Of course this all very subjective but I though I'd just share my experience here. The greater majority (with some very notable exceptions, for ex. "PansyTart's measuring system") recommends: A-Ring: OK if you can just fit one finger under the ring. In my experience this is just fine. Though 2 fingers is quite confy but there the pull-out danger definitely exists (though not accedental). But now matter how small you make the ring, that snake can be pulled out unless it's secured by other means. Any great tips from non pierced 'members' (a part from the usual POI, KSD-like things)? B-Ring/Cage/Tube: OK if 'snug'. In my experience here I'd disagree and would rather recommend 'loose'. My latest cage is 3mm wider than the measured diameter. In my opinion this is not snug (which would be cage diameter = measured widest diameter). If you're really flaccid you will 'float' in the cage (that can feel a bit weird) but at the slightest sign of growing (or showing?) you'll fill the cage (= become snug) which for me seems to issue a signal: "Stop! Grow no further!". And then it's very confortable. The device doesn't slip or gets pushed away from the pubis. Length: flaccid length minus 'something' Like for the B-Ring in my experience this would rather be 'flaccid length plus something'. My cage is 3 to 5 mm longer than the measured flaccid-rest-length. Like for the diameter, this leaves some space for growing but not too much. Gap: +/- 10mm OK. Though with the little 'extra' space (in diameter and length) in the cage, a soon as the slightest growing sets in the cage will be filled and the whole device fits like a sock and does not need a very narrow gap to stay put. With my previous devices I had serious problems with the too small diameter of the cage. My hypothesis is that given that I could not grow by even the smallest amount in the cage it would start growing in lenght pulling the cage away from the body causing the well known stretching and burning. Even a larger ring would hurt during the nightly woodies. For me a cage that allows for some growth is just perfect. It seems so me that if the growing is allowed to some extent it stops once it hits the inside of the cage. Now the night-time erections are not as bad as in a smaller cage. By the way, night time erections are often called morning wood. Me, I'd rather call them night concrete (not only harder but also longer and thicker) and they last... but safely locked up that's is all for nothing... Anyway, with the sizing of my latest cage I'm very happy. Have fun!