The tip I use the most to spray BIN on cabinet doors is a 310 tip. I use the green FFLP spray tips from Graco. For oak, BIN is very thin and fills in the grain cracks pretty good even without filler, but not completely with spraying alone. Spraying the oak cabinet doors on a flat surface, using a 310, or a 312 tip, you can build up the primer pretty good to fill a good amount of the grain holes, but some deeper cracks will remain. What I do is I spray one coat of BIN first, so I can see the remaining cracks easier, then I fill those cracks with grain filler, sand, and I spray a 2nd coat of primer. Then I apply two coats of paint. This will smooth out the oak, but it's very difficult to completely eliminate the natural grain pattern. The cracks in the wood pores though will be gone doing it this way. This also prevents having to use a grain filler on the entire surface of the doors. You only have to use it between prime coats where needed.