(Jon of the Clue Crew reports from Steinway and Sons.) It's the ten-letter term for the piano's diaphragm; it's made flexible enough to vibrate, but strong enough to handle a thousand pounds of force from over 200 strings
.... -Mr Beal stated his terms in a letter ..... 
LADIES' FLEXIBLE SOLED SHOES 12s 6d, 13s fid, 14s 6d .....