A stainless SUS303 adapter taking an AN3 line onto an M10x1.0 metric thread — probably the single most-encountered metric brake port, appearing on countless callipers, master cylinders and unions. It is the standard route to fitting braided AN3 brake and clutch lines to a metric vehicle without modifying the original components, and it can be removed later with no trace. SUS303 stainless resists the corrosion that plagues fittings mounted low in a wheel arch. Pitch matters more than diameter here: M10 ports also come in 1.25 and 1.5, and all three will start into the wrong fitting before damaging the thread, so gauge the port first. Once fitted, bleed the circuit fully and check the joint for weeping under sustained pedal pressure before road use.