Those four blue poppets on Ebay are BALANCED poppets, the older style balanced poppet that are screwed onto a tiny stainless steel shaft which has one visible o ring and another inside the poppet itself. These were used for a number of years, replacing the unbalanced Duro poppet. These old style balanced poppets were original equipment on the balanced 156 version of the older 109 first stage, and work just fine, but are not interchangeable in any way with duro poppets. The blue balanced poppets on ebay use a balance chamber over the spring, not a disc like the duro poppet uses, and the spring is different, with lighter tension. A third poppet currently in use is the modern S poppet, exactly what the 250v uses. The S poppet is one piece, no separate removable shaft, two o rings on the poppet stem and an easily replaced seat. Older 250 scubapro second stages used the blue balanced poppet like the 4 being sold on ebay. Those 4 poppets are useless if you dont have the stainless steel shaft they must be attached to. Again, those are balanced poppets just like the listing states, NOT duro poppets and not useable without the shaft and correct spring and balance chamber. I'm a great believer in doing your own service, but you have to be careful and know what you are doing.
