Kit one used in a piano piece (American) (9)
I believe the answer is:
Here is my best explanation:
'kit one' is the definition.
'apparatus' can be an answer for 'kit' (thesaurus). I'm not sure about the 'one' bit.
'a piano piece american' is the wordplay.
'a piano piece' becomes 'apparat' (I can't explain this - if you can you should give a lot more credence to this answer).
'american' becomes 'us'.
'used in' is the link.
(Other definitions for apparatus that I've seen before include "Equipment, device", "political organisation", "Kit", "Technical equipment", "Collection of equipment designed for a particular purpose", "Tackle", "Set of equipment serving a specific purpose", "Equipment, gear", "Machinery" and "Lab equipment".)