Howdy,
What is the proper fingering to gat a C Natural on a D whistle that has a thumbhole?
Sincere thanks,
K.S.
thumb up XOO OOO
bee sharp
I’ve considered getting a C thumbhole on my next D whistle. Aren’t the two reliable ways of obtaining C natural as follows: ooooox with the thumbhole uncovered, and oxxooo with thumbhole covered?
Denny has it right. With the top finger down and thumbhole closed, you would be venting at the second top hole and creating a B. But if you have the thumbhole open, you are venting just above the usual hole and playing the C natural.
Of course, you don’t have to use the thumbhole and there may be some interesting combinations depending on the whistle.
think first open hole, not last closed 
Exactly!