Rodney,
The #9 and D-9 great machines, very smooth and quiet, great stitch, and well worth buying if the opportunity presents itsself. Like Joe says the Singer 9W-1 and 9W-7 is Singers continuation of the model after they took control of W&W in 1905. Some of these 9W-7's use a featherweight bobbin which is of great convenience as the donut bobbins for W&W's sell for between $10-$20 each on ebay. The 9W-7 was replaced by the Singer 115 around 1913.
The difference between the #9 and D-9 is the method the bobbin is held onto the bobbin case. There is a Wheeler and Wilson Yahoo group which has a wealth of information in it's files and conversations:
http://groups.yahoo.com/neo/groups/W...tions/messages
Jon