I looked at topic filter in WM yesterday. The recess of the inlet hole area is actually deeper than it appears in the pics. It now reminds me of the Fram 6607/7317 series with one big difference. The beveled thread boss is 'imo' a much better design than the Fram. That said, at ~$10 WM price have to go with an Ultra. If I could get them for $5-6, I would be interested. Someone posted XOM sometimes has a rebate making them that price. Have to watch for that.