The early European cars used a different standard for their lighter sockets.
Here are the sizes
12 volt cigar lighter receptacle and plug, size A
Receptacle inside diameter: 20.93 mm to 21.01 mm (median 20.97 mm)
Plug body diameter: 20.73 mm to 20.88 mm (median 20.805 mm)
Most often used in American automobiles.
12 volt cigar lighter receptacle and plug, size B
Receptacle inside diameter: 21.41 mm to 21.51 mm (median 21.455 mm)
Plug body diameter: 21.13 mm to 21.33 mm (median 21.18 mm)
Most often used in European automobiles, and sometimes as a second socket in American automobiles expressly for DC power connections.
Saab used to make a slip on adapter years ago but I have not seen one in ages.
