Does anyone know definitively what the diameter of the hammer knuckles
(rollers) should be on a Steinway model "O" Duo-Art grand? Surprisingly,
Steinways say they are uncertain!

Almost all "O" Duo-Art grands found here in the UK were made in
Hamburg, but their extended-key actions, which were installed here,
seem invariably to have been made in the US and thus have different
dimensions from the German actions.

New York-dimension hammer shanks are available with both 9 and 10 mm
diameter knuckles.  I intend to renew a set on a 1924 "O" Duo-Art grand
whose original knuckles were replaced -- perhaps incorrectly -- with 10
mm knuckles.  Probably they ought to be the same diameter as those on
a late US model "O".

The difference in size may be immaterial, but some technicians maintain
that original 9 mm knuckles give a correct lighter, cleaner touch.
Ultimately I may have to pull the action and experiment before ordering
a set, but any information in advance would be appreciated.

Patrick Handscombe
Wivenhoe, Essex, UK