Does anyone know what kind of pen this is? It is 12 cm long uncapped. The cap says Conway Stewart on the clip, but it does not fit, and I doubt it was original. The pen is 12 cm long with a distinctive ink window and a hooded nib. It resisted taking apart, and I did not force it. It is a piston filler with blind cap covering the screw mechanism. The knob of the cap is set a bit off center, and moves what looks to be a white plastic piston. It works, or at least it draws water. The only marking on the pen is 732M incised on the barrel just above the blind cap. Attached are three pictures.