Simplifying this effort even more, the filter mount is drilled with basic 1⁄2-inch oil passage holes. These can be tapped for either a 1⁄2-inch pipe or a -10 O-ring seal that is 7⁄8 x 14. For 1⁄2-inch pipe, use a 23⁄32 drill bit. The -10’s 7⁄8 thread requires a 13⁄16-inch drill bit. The larger sizes more closely match a -10 AN hose, which has a 1⁄2-inch inside diameter.