Need to connect an in-line duct fan to a ductstat. In line fan has white (common) wire - black (hot) wire and green (ground) wire. Ductstat is a 110 A/C outlet. Need to make a plug from fan - which will connect to ductstat

It sounds like you are making a plug from the fan to plug into a receptacle. I that is so:
Wide prong = white, neutral, common
Narrow prong = black, hot
Ground prong = ground, green, bare

No - I need to make a plug for the in-line fan units to be connected to the ductstat which is a 110 a/c outlet with a fuse. I guess it does not matter weather I put the black and white wires as long as the green goes to ground. -

Bones had it right.

Wide prong on the plug to white or common of fan
Narrow prong on the plug to black or hot of fan
Ground prong to green of fan

EPM