We've been unable to find the good ol' cast iron housings.  We don't like the mess the aluminum ones make.  Besides, the Interceptor can make enough messes on its own without the help of an aluminum housing/neck.  Why call it a neck-'cause you can wrap something around it tightly?  So for now it's aluminum or nothing. These are made of solid billet and look like a piece of art!  No. 28 in the photo.