This steel adapter has a female 18x1.5mm inverted flare (convex seat) on one end and an 8AN male (3/4-16, 37° convex) on the other. The two-piece design allows you to hold the adapter while screwing down the female threads. This avoids damage to the sealing surface, but requires the correct concave seat on the male fitting. It cannot be used with a crush washer. Sold individually.