[denniskliesen]

The original Model A bolt is 7/16-14. The guide online for installing an oil filter recommend drilling the block to the size required for a 7/16” helicoil. Then tap the threads for a helicoil that is 14 threads per inch. You do not use the helicoil if installing a filter, but if you decide to remove the oil filter and install the original hardware, then you install a helicoil and the original bolt. Whatever works best for the user as long as all passages are at least 5/16” from the fitting where the oil exits from the middle side of the block through all of the fittings and filter head to the point where the oil returns to the oil galley.