Heavy Duty One Piece 100% Stainless Impeller Housing The stock OEM units have an aluminum housing with a thin stainless liner. Over time they can "bubble" or swell due to corrosion between the aluminum housing and stainless liner causing contact with the impeller and eventually jamming the impeller. The one piece stainless housing solves that problem. It is an excellent choice for stock to highly modified watercraft and especially watercraft that operate in salt water. Direct replacement for Yamaha #66V-51312-00-94 #66V-51312-01-94. Please use compatibility chart above for exact fitment. Message us with any questions. This is the stock 155mm size wear ring.