- Manufactured in high quality stainless steel, these items have very fined slots along their length along oil to pass through but trapping any swarth or debris - Screws into the base of the timing case on all post 1931 SOHC engines - Not easy to manufacture, which I'm afraid is reflected in the price - For my own racing machines I tend to reduce the head of all the bolts, including this filter bolt, so I have made some of these for sale. They do not really save much weight, but they do look nice!