This straight adapter mates an AN4 37-degree male flare to an M10*1.0 male metric thread. The fine 1.0mm pitch distinguishes it from the coarser M10 threads, so check your port carefully before ordering: M10*1.0, M10*1.25 and M10*1.5 will all start in the wrong hole and none of them will seal. M10*1.0 is common on turbo oil feed banjo bosses, small sender locations and metric brake and clutch components. Paired with -4 AN hose it suits turbo oil feeds, gauge lines and low-volume circuits. The AN flare seals dry on metal contact; the metric end relies on the sealing washer or O-ring the port was designed around.