16" records. The ones I've got were cut at either 78 or 33, so they
could be replayed on any turntable. Not really vinyl, they're acetate
coated aluminum discs. Usually with a second hole near the center for a
drive pin to fit through, so the disc doesn't slip on the platter when the
cutting head is in place. You can tell when there was a new engineer on
duty, he drops the cutting head so the stylus cuts through the acetate
into the aluminum.

In later years, 1950's for example in Australia, 16" moved from acetate
coated aluminium to vinyl same as LPs. 16" can be played on turntables only
if you have a long tone arm placed further away from the spindle otherwise
the disc will cover the tonearm. A standard record player will not play
16".

Ian