The 139. The iconic Fountain Pen, that I would be OK to say that is one of the grail pens for vintage and even modern MB collectors alike. This is a L139G in celluloid.
1: Meisterstuck or Masterpiece that means first grade
3: piston filler of the 30s
9: 9 size, the biggest of this series starting from 2, so we have the smallest K 132 ( K standing for kurz meaning short), 132,134,136,138 and 139 which has the L in front meaning like long or luxury and if it has a G that means in this case that it comes with a gold nib , mainly the celluloid ones from the post war era.
This pens trim is in great condition, not mint, but I would rate the trim excellent. The blind cap has a B for nib. It uses a telescoping piston filler. The Cap has a MW in a circle, of which Im told is a company that gave lots of pens out to their employees. The star is in excellent condition as well, it have a very nice aged look. The gold nibs plating has faded a bit, as you can see in the pictures. Also the window is not perfect, it has some fading of the lines as you can also see in the pictures. The nib is very nice and flexible, one of the nicest flex nibs for a XX9 nib Ive tried in a while.