The majority of plates you will find are level III and meant to be run in conjunction with soft armor backers. There are indeed level IV plates that do not require backers, however I would much prefer to run a backer even with a level IV. If you are going to be buying ceramic plates second hand I would be cautious, and make sure the seller is trustworthy. If ceramic plates are dropped or even mishandled they can crack, which extremely degrades the ballistic integrity of the plate. These might be non-visible cracks, completely unnoticeable to a prospective buyer. You can always get them x-rayed to check for cracks, but that is a bit of a PITA... You can generally find steel plates for much cheaper, and also with no worries of cracks... They will be heavier though. Armor is one place I wouldn't want to cheap out. IMHO
Last edited by Aftermath686; 02-18-2011 at 2:31 AM..