CB series chastity cage.

Hey! I'd like to know if there's an average size penis best first a certain middle, I know there's the 6000S, although what size penis can this accommodate? And how do I work out which model I need?

Hey ouhgoiuh

You'll need to measure your length and girth whilst flaccid and then take a look at the measurements on the product description to figure out whether the cage will fit you comfortably, whilst still stopping erections. 

You can find dimension details at the bottom of the description. The CB-6000S you've mentioned is their smaller design, and has an overall length (including the top ring) of 3.5 inches. The cage portion has an inside length of 2.5 inches. If your flaccid penis is longer than 2.5-3 inches when measuring from the pelvic bone, I would recommend going up a size to the CB-6000 for extra room. 

Your cock cage should be comfortable, breathable and non-rubbing, but still stop you being able to get an erection.