Ok - I found my notes:
ANSI #40 chain and sprockets have the same pitch as bicycle chain (1/2 inch), but the sprocket (and chain) is "thicker" than a standard bicycle sprocket and chain (almost twice the thickness, IIRC). So - I had purchased a 9-tooth sprocket (with a 1/2 inch bore for the shaft of a motor I was going to use) and had the sprocket face ground and chamfered to the size needed for the bicycle chain.
Now, if you are using #40 chain with the #40 sprocket, no need - just know that the chain won't fit a bicycle sprocket well (it will probably work, but it will have a bit of side-to-side play on the sprocket itself, which could lead to issues).