Hi- I am restoring a National sidecar to fit on my 16J. Unfortunately all the attachments on the bike have been lost at some stage over the last 100 years (last 70 yrs in storage at various locations) but the bike and sidecar was a pair when delivered New and used as a combination. The National sidecar has the type of 2-piece clamp with two hemisperical shaped elements which are pressed together With a bolt and a set nut. This means that the attachment connected to the bike (front frame tube and rear axle attachment) should be ball connectors. Harley did this the opposite way and had a conical arrangement with the hemisperical part connected to the frame. I will probably have to make ball attachement to the bike frame based on some Harley mounts and do some milling, drilling and welding UNLESS there are somebody out there which happen to have such attachements for the frame lying around or could provide pictures/drawings/advice of such attachements for the National sidecar. I have seen a National connected to a Thor and an Excelsior but did not succeed in getting in contact with the owners.