Model 40
Very first design.

Model 40A
Another design made in 1927.
It had new engines and a cabin which could carry two people.
25 of these were made.

Model 40B
These were Model 40As with a new engine.
Their name was changed to Model 40B-2.

Model 40B-4
Model 40-Bs with a bigger cabin which could carry four people.
 It had windows which could be opened.
38 of these were made.

Model 40B-4A
One Model 40B used by Pratt & Whitney for testing.

Model 40H-4
Four Model 40B-4s which were made by Boeing Canada.

Model 40C
Similar to the Model 40B-4, but it had the same engine as the Model 40A. 10 of these were made.
Model 40
Very first design.
Model 40A
Another design made in 1927. It had new engines and a cabin which could carry two people. 25 of these were made.
Model 40B
These were Model 40As with a new engine. Their name was changed to Model 40B-2.
Model 40B-4
Model 40-Bs with a bigger cabin which could carry four people.  It had windows which could be opened. 38 of these were made.
Model 40B-4A
One Model 40B used by Pratt & Whitney for testing.
Model 40H-4
Four Model 40B-4s which were made by Boeing Canada.
Model 40C
Similar to the Model 40B-4, but it had the same engine as the Model 40A. 10 of these were made.
Boeing Model 40