Metal clarinets are quite commonly used as "school instruments," although the plastic ones have pretty much displaced them in the "new instrument" area.

The Ohio Band Instrument Company was active in the 1950s, I believe; although I don't have records at hand to verify this. I know that I saw some of their instruments in that time period, but I don't know how old they might have been then.

The preferred material for "performance grade" clarinets has always been wood, although the newer plastic models may closely simulate the resonance of wood. Until about 1955?, when Selmer introduced the "Bundy" plastic model, metal clarinets were produced primarily as "student" and "marching band" models. Wood does not stand the rigors of hot breath and frigid football stadia very well, and people were reluctant to expose their good grenadillas to such conditions.

There was also the belief that the metal clarinets stood up better to the rigors of young student use - and they were considerably cheaper than a decent wood model, which was important if you were equipping a Jr Hi or High School band.

True "C" clarinets are very rare, with "Bb" being the most common. "A" tunings are/were made for "orchestral" work, and wooden (or plastic) Bb clarinets could be "played in A" by substituting an "A" neckpiece (the short piece that the mouthpiece fits into). Some "better grade" wood clarinets are sold with both necks. Intonation is generally a little better in one or the other of the two keys, but can be acceptable for any but the most finicky concert performance.

Since the metal instruments were used almost exclusively as "marching band" or "student" instruments, it would be exceedingly rare to find one in any key other than Bb.

The clarinet is fully chromatic, and can play "all the notes." It can thus be played in any key.

Compared to a flute or pipe or pennywhistle, the clarinet is a fairly "high pressure" instrument, so even minor leaks at the pads or corked joints can produce rather horrendous squawks - one of the reasons many people consider it a little more difficult to play (well) than some similar instruments.

There have been a number of "historical" changes in key mechanisms that can be used to "date" a given clarinet fairly accurately, but "hands-on" examination - and the appropriate reference books - would be necessary for any meaningful guesstimates.

A quick comparison with a "modern Boehm" clarinet would indicate whether the instrument is pre - 1930 or so, since that's about the time when the "modern" mechanisms started showing up. Dating anything earlier may be more difficult.

John