Hello Martin Tengström and MMD! Thanks for confirming the fact
that the discs for the 28-note Nystroem's Reform Organ and its lesser
relative, the 24-note Complett Organ, such as you describe it, actually
are the same diameter, that is 36.5 centimeters, or approximately
14-1/2 inches. Consequently, it would be interesting to know if the
24-note scale is incorporated within the 28-note scale [as a subset];
that is, if it would be possible to play the 24-note discs on the
28-note organ (or inverse, with a loss of four notes, of course).
To make things worse, there also are Nystroem-type player organs using
24-note 33-cm (13") Ariston discs, with somewhat enlarged driving holes
(10 mm instead of 6 mm). You can see and hear some video clips of my
Lindahl organ at YouTube: http://www.youtube.com/tussetuss .
Ariston discs are made of a material with a thickness of about 1 mm
called "Pressspan". (Oh yes, that's how it is spelt in the new German
orthography!) [I think the word looks nicer when spelt with the s-zet
character of the old German orthography: "Preßspan"! ;-) -- Robbie]
With some luck, you can find it in artists' materials shops. Most
probably it will be only one-half-millimetre thick which, on the other
hand, causes less friction and actually would improve the performance
of a carefully adjusted organ.