This may help.

http://shop.industriebedarf-beilke.de/artikel.php?name=6kt.-Mutter-DIN-6331-M-10-SW16-A4&action=show&artnr=11603010&SessID=6e38fc91335fd910936f0915b236d427

Steve

On May 8, 2013, at 10:38 PM, Bill Monk wrote:

> It's a 10mm lock nut but not sure about the thread pitch. I can tell you 
> tomorrow. I have a couple in a bag
> that I can check.
> It should be  easy enough to find at a local 
> hardware store. I wonder if the SW
> has something to do with it being a
> lock nut.
> 
> Bill
> 
> Sent from my iPhone
> 
> On May 8, 2013, at 9:25 PM, Bryan Feddish <uprightbassghost@HOTMAIL.COM> wrote:
> 
>> Can someone tell me the size of the nut (Item # 7 ) at the bottom in this picture?
>> 
>> http://tinyurl.com/cayakoz
>> 
>> Thanks,
>> Bryan