Brake Cylinder FAG 31

[rishik]

I am trying to replace the wheel brake cylinders on a 1986 Audi 80 1.8 (Carb) GL. I am pretty sure its the series 2 (the one before the new model was also launched in 1986). But I am so confused, everything I look at points to them being 14.3mm bore, however when I called the shop with my reg they said it was a 15.9mm!? All thats written on them is FAG 31, and as they are still in the car I can't measure before buying. The rubber covers have these numbers 331611695 and R1759.

My next question, does anyone know the size of the bolt that connects the brake line into the cylinder - I've been trying a 11mm spanner but it seems to be stripping the bolt; is it imperial?

Thanks so much for reading - I am totally confused, and any advice would be greatly appreciated!