I have often had confused customers coming in to IFS looking for cork grease for their flute.  And I end up confusing them even more when I tell them it isn’t recommended!  Cork grease is meant for….you guessed it, corks!  And modern flutes do not generally have corks.  (We do carry it for piccolos, which often do have corks.) However, it seems logical to add lubricant when two metal pieces that are supposed to fit smoothly together no longer do so.  In fact, this is the case for many brass instruments.  But flutes are different.  The reason cork grease isn’t recommended is because the tenons (joints) of the flute are very closely fitted by the manufacturer.  Unless something causes the tenon to go out of round or it gets dirty, the tenons should fit together very well without any type of lubricant.  Adding grease can actually hurt the flute over time.  Grease can trap small particles that will grind into the metal every time you put together and take apart your flute.  This can wear down and scratch the tenons, requiring repair. If the tenons are too tight, wipe them down using an untreated cleaning cloth.  Be careful not to swipe the edge