Metric-standard rail meets tight geometry as often as any other, and the 511/424 is the flange for that meeting. It carries 1.67-inch OD tubing in a full collar with a set screw lock, but the base is trimmed on two sides so it can seat on a narrow ledge, tuck into an inside corner, or sit beside a second flange on a shared post. The collar height matches the round-base 510/424, so the two mix on one run. It comes in 316-grade satin stainless steel. The grade suits the projects that specify 42.4 mm rail in the first place: promenades, pool decks, and coastal buildings where salt and chlorides pit 304. The satin finish keeps glare down on an exposed edge. Pair it with the matching 1.67-inch tubing, facia mounts, and welded floor flanges in the 316 family. Ships from US inventory.