This is ARC X-Low Shock Piston 1.1mmx4 OD 11.0mm (4).
The new shock pistons for X-Low shock in 11.0mm diameter Compared with R134002 it is 0.1mm smaller, shock holes remain 1.1mm X 4 holes.
New piston gives smoother operation and a lighter damper effect with the new piston, the chassis will roll more with the same shock oil.