No. L 129
The 12x was produced for only a short time from around 1935-40. The L129, in particular, seems to have been produced after two or three years of success from the smaller sizes. Collectible Stars I scores the L 129 a 9 out of 12 points in rarity. From my experience, it is far more difficult to find (and afford!) a 129 in comparison to the 139. As seen in this advertisement from the late 1930s, the 129 was priced at RM 50. Compare this to the RM 45 price of the 139 in catalogues around the same time.
A beautiful L 129 belonging to specialk0449
A beautiful L 129 belonging to Joudenali
When I held the 129 in my hands I was surprised by its size. I was expecting it to be as large as the 139, but it was very apparently smaller. I don't like big pens and so the 129 was a perfect fit for me, but I was confused by the fact that it was so much smaller. In the pic here, you can see what I mean. The 129 measures 12.8cm capped, the exact same as the 136. Also, the 129 measures the same size as the 128 - the clear difference between them is that the silver rings are only found on the 129. Also, it is interesting to note that the 129 and 128 have the same nib size - a '245' or size 8 that is found on the 138. The 139 nib is larger.
The L 129 is a push-knob filler or Stoßfüller. This uses the same idea as the button filler, but instead of removing and setting aside the blind cap, here you simply loosen and then push the blind cap itself to engage with the pressure bar inside. MB advertised this system as being so efficient that it required only one hand to operate. The Stoßfüller was used on higher-end MB pens.
The bi-colour nib on the 129 is made of 14c gold. While the 13x series pens were found with a variety of nibs like gold, steel, and palladium, the 12x series pens were found mostly in gold because this model was produced before WWII and hence did not experience any restrictions over the use of gold.
Finally, the 'L' in the L129 stands for Luxus or luxury.
L to R: 138, 129, and 139 belonging to specialk0449
L to R: 129, 128G, 128S, 128PL belonging to Joudenali
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