I think a B6 would probably fit, but a B3 is the right model for a Jet. (EDIT: I just got out the measuring tape. A B6 would fit below the bridge, but not below the stoptail holes. So it would be too long to use a Towner bar. You definitely want the B3.) For reference, here's my 5620 (with a B6C) on the left, next to my Jet (with a B3C) on the right.