In the late 1940ies, FHF released a manual wind movement in a contemporarily modern construction with directly driven center second. This caliber 25 (and its twin FHF 28) had a diameter of 10 1/2 lignes.
The nomenclatur of FHF was in a way, that an additional "1" at the end marked the same movement, but with a larger base plate, and so, the FHF 25 was transformed into the FHF 251 described here with a diameter of 11 1/2 lignes.
The specimen shown here is in a red-gold tone, visually very nice!
On the base plate, you can see the larger diameter, whose additional outer area isn't used.
As on most movements of that time, a two-storey construction is used, with a minute wheel, which is beared under an own bridge. The third wheel at 4 o'clock is connected to it and drives the central second wheel.
This classical gear train builds pretty high, but allows large wheels, a large mainspring barrel and so allows better precision.
In the specimen shown here, there's a golden toned two leg Glucydur screw balance, which is located in two Incabloc shock protection bearings. It beats with 18000 A/h and regulates a classical swiss lever movement. For adjustments, there's a long regulator arm with scale on the balance cock.
On the dial side, this movement is stamped as "FHF 25", which makes the correct identification quite difficult. Apart from the larger diameter of the base place, the movement is identical to the FHF 25, so for a watchmaker, it doesn't matter, whether he orders parts for an FHF 25 or an FHF 251.
Of course, this movement has got a yoke winding system. The escapement wheel bearings are topped with cap jewels. It's hard to find better made movements than this.
In the lab
The specimen shown here was resinified and came in a damaged and rusty case into the lab, so it only got an oil treatment to bring the movement back to life. With an amplitude of now up to 260°, this is perfectly OK for the archive and so no further service was neccessiary.
This movement and watch is a donation from Erwin. Thank you very much!