This is a genuine BMW lock Ring, part number 11 25 2 247 534. The number stamped on the part is 11252247534; BMW's catalog files it under the short number 2247534. You will find it on our Engine shelf, under Piston with rings and pin.
It fits every E46 body style (318d, 318td, 320d, 320td and 330d, 1998–2005), with the M47, M47N, M57 or M57N engines.
BMW draws it on 3 diagrams, among them Crankshaft-Pistons (11_2097) and Crankshaft-Pistons (11_2321).
We have not had one on the shelf yet. Request it and we will tell you when one comes off a car.