I'm looking into fitting a "pancake" DC motor to power an old Aeolian
Pianola (USA) spool frame.  I measured the sprocket gears and ladder
chain and shafts; none of the dimensions seem related to either English
or metric units.

The Aeolian sprocket hub is bored for a shaft of 0.204 inch (5.18 mm)
diameter.  The measured chain pitch, which agrees with the sprocket,
is 0.282 inch (7.17 mm), or 42.5 links per foot (139.4 links per meter).

Why did Aeolian, and maybe the entire industry, use these unusual
sizes?  Is (was) this ladder chain pitch an old industry standard?

MMDigest articles of several years ago say that Boston Gear Co. used
to supply the same chain as used in player pianos.  What was Boston's
designation?  Were other sizes used in player pianos and orchestrions?

Robbie Rhodes
Etiwanda, Calif.