Date: 1934. Image by VintageSax
Instrument is silverplated, and has rolled tone holes. Models after 1948 don't have rolled tone holes. These instruments are sometimes called "Naked Lady" models or "M" models. The "Naked Lady" refers to the engraving often seen on the bell. There is a misconception that the presence of the Naked Lady engraving and how much of the Lady is visible is an indication of the quality of the individual instrument. Noted Conn researcher Dr. Margaret Downie-Banks says that there is no truth to this. In its catalogs Conn called these saxophone "Standard Saxophones".
The issue of mouthpiece selection for the 12M in relation to intonation regularly comes up in various forums. The concensus appears to be that the 12M is quite mouthpiece sensitive and works best with a mouthpiece that has a large, round chamber. This is in accordance with the type of mouthpiece most in use at the time.
What Conn said in 1939:
Whether you are interested in the alto, tenor or baritone, when you buy Conn you can be sure of getting such important and exclusive improvements as Hydraulic Expansion; drawn-rolled tone hole sockets, that will not leak or cut the pads; adjustable pivot screws, that will give light, positive action and will not vibrate out of adjustment; Red-O-Pads, that will increase resonance and add brilliance to your tone; new, hard keys, that give that confident "feel" when you touch them; reserve power - that extra "sock" and "kick" produced without straining; new design octave socket, that helps "buzzy A" and gives quick response and brilliance to upper register; raised high E key; and others. On the alto and tenor you have also the C-D trill, G# trill, new table keys - all three patented and exclusive on Conns. On the alto you have tuning device and bottom mouthpipe key - two more patented and exclusive features. Steelay mouthpiece standard.