Ad. Sax jr. 12023
Now, a Sax junior is not exactly the kind of horn that you treat lightly, and yet...

The original register mechanism, in which a balance of spring tensions managed the switch between the lower and the upper register key, was replaced by an ex–Buescher C-melody mechanism, which is faster and more reliable. The spatula for the left thumb still is original.
This mechanism also offered a beautiful opportunity to implement a C#–correction.

The C#–correction mechanism on the front side. The mechanism closes key nr. 18 about halfway. This key has a small disk hanging under it (red arrow), which takes care of the desired correction. The extend to which the key actually closes is not that critical.
Ergonomics: another spatula for X (top F) and a higher one for C1 (palm D). These parts were made entirely anew.

An extra register hole placed lower along the tube makes it possible to securely octavate the bell tones Bb through C#. This offers an acoustical interesting alternative to the notes obtained by the ususal fingerings – an idea that Sax already set forth in his 1866 patent.

Yet another idea of Sax sr. from the 1881 patent: an altenative for F# for the second finger right hand (red arrow). The mechanism closes key nr. 10 only (green arrow) and produces an F# which is only very slightly on the sharp side. In some combinations this fingering works even better than the regular Tf (side F#).