It is the Auction Number 4614198096 on German Ebay
I also found a shop on US Ebay that sles them:
http://stores.ebay.com/POWERSPARKS The US Number Codes may be different from the German codes.
Here is the plug I use in the 235
W R 78 G
It goes like this:
W = Thread diameter 14X1,25 wrench size 21
R = Resistor
7-8 = Heat range
G Thread lenght 12,7
Instead of WR78G you can also take a
FR78G. You only need a smaller socket.
Also you may skip the Resistor F75G
The important numbers are only Heat range and thread size.
An aditional X/W or Y marks the gap size 0,.9/1 and 1,1 millimeters.
Hope this helps.
If you can`t get em I may buy some and send them to you if you want.
Good Luck, Frank
