Well, actually, I didn't ask the right question. I want to make some buttonholes on some masks and didn't know which one to use on the 401. Now I know. Andy Tube to the rescue, as usual. (This is assuming the parts are in the box they came in.)
The 301 uses the red boxed one:
The 400, 500 and 600 machines use the one with the sewing machine pictured on the box:
The 700, 900 and 2000 series use the one with multi-colored squares on the box.
( I tried to put the pictures under the description, but QB was having none of it.)
bkay