A strikingly thin ballpoint with a twist mechanism and a matt, silver-coloured surface belongs to the Montblanc Slim Line. Under this name Montblanc carried for years a range of emphatically slender writing instruments which stands clearly apart from the Meisterstück programme in diameter alone.
There are Slim Line ballpoints that take two short refills in different colours, usually black and red. Short refills from other makers can also be fitted as replacements; pens bought second-hand therefore often contain refills of another make, which says nothing about whether the pen itself is genuine.