@Mikey B - I don't know about the Conn 10M necks being tapered into the receivers. I haven't seen any - but obviously that doesn't mean they don't exist. Taking measurements from different examples using a digital calliper would likely answer that question. Thing is, the Conn 10M was in production for a long, long time in saxophone terms and the design was "tweaked" as the years passed. Conn started out "true" 10M production with very late-model "Transitionals" in 1935 - and these are Conn 10Ms in all but name. To claim they're not really Conn 10Ms is being overly pedantid, because the only thing missing is the "10M" stamp near the serial number - which really is splitting hairs, eh? So, the Conn 10M versions with rolled-toneholes started in 1935 and went right through until the non-rolled tone-holes models began to appeari in 1947. Later, the neck design changed into the double-socket neck models in 1956, and finally into the (and I'm not kidding here!) underslung double-socket neck designs circa 1962, with sheet-metal keyguards. Yes, the final production Conn 10M tenors really did have underslung necks, just like Conn 6M altos. Here's an example:-Tomasz, thanks for the information you have provided here, that's very interesting. It's definitely something for me to think about at some point in the future. Perhaps you can clear up one issue. it's been suggested to me that some of the Conn 10m tenons were slightly tapered into the receivers is this true? Also, I'm guessing as you are passionate about Conns as I am about S20s you must have some of these saxes then? If so could you perhaps post some neck photos from varying angles if you get the chance?
An interesting fact for a would-be Conn 10M neck manufacturer:- the neck from a student-grade Conn 16M dating from the 1950s will fit (and play quite nicely) on a pre-1956 Conn 10M. Therefore, if you ever made a "quick & dirty" prototype of a Conn 10M neck for proof-of-concept purposes, you could make a swift start by replicating a Conn 16M neck from the 1950s. Of course it's a single-socket neck and the decade it was made is important. I'm not claiming that a Conn 16M neck is just as good as an original Conn 10M neck. I mention it purely because it's compatible. Be aware that Conn 16Ms made during the 1960s were made in Mexico and are referred to as "Mexi-Conns". There's not much love out there for Mexi-Conns because by then Conn had gone into a major decline. However, please note that all Conn 10Ms and 6Ms (whether produced in 1938 or 1968) were made in Elkhart, Indiana and not down in Mexico. Whatever, here's the proof that a Conn 16M neck on a Conn 10M is viable:-
Making necks for double-socket Conn 10Ms would obviously be much harder than for standard single-socket necks. Bear in mind that for any owner of a, say, 1959 Conn 10M that's missing its double-socket neck, there are simply no viable options out there other than to get another Conn-made neck of the same vintage. They either have to somehow track down a double-socket neck for their horn (which could take 20 years!) or regard the saxophone as a "wall-hanger" or donor horn for spare parts. Suffice to say neither of these are attractive options...
People get very worked up about how Conns with rolled toneholes (pre-1947) are much better than the ones without. I've got both types so am agnostic in that respect and don't want to start a bun-fight. All I can tell you from personal experience is that regardless of when they were made, whether it be 1935, 1955, 1961 or 1967 - all Conn 10Ms and 6Ms are professional grade horns through and through. They all come alive in your hands and start to "sing" - just like all pro-grade horns should. With that said, in purely financial terms, if you're looking for the "sweet spot" then you'd probably do best to concentrate on making replacement single-socket necks - because (in the eyes of owners/collectors) these are more sought after and therefore regarded as more valuable. To be honest, the later double-socket Conn 10Ms don't get the same attention/respect (particularly not the ones with underslung necks and sheet metal keyguards) - but they are still good players.
As regards providing photos of Conn necks, I'll send them directly via your website. Only thing is... our house is undergoing alterations at present so all my horns are piled up in a large stack of cases inside a small room. Bear in mind that I'm a saxophone collector, so it's a very large stack of horns! Getting to all the Conns would be a major pain. However, I've just checked and there's definitely a 1952 Conn 6m (no microtuner and is awaiting an overhaul) at the top of the stack, so I'll send you some photos of that one. As a bonus, I'll even include neck tenon measurements taken via a digital calliper. The other Conns are lower down in the stack and to be honest I don't want to disturb them. The good news is that Google images is your friend in such situations:-
Various photos of Conn 6M necks
Various photos of Conn 10M necks