The price stated is for per pieces of spark plug, do drop me a msg if you are unsure if your Opel model is 3 or 4 cylinder. 
Shell
Thread Diameter
12mm
Thread Pitch
1.25mm
Seat Type
Tapered
Reach
25mm (1")
Hex Size
9/16" (14mm)
Terminal Type
Solid
Gap
.028" (0.7mm)
Center Electrode
Material
Iridium
Type
Fine Wire
Size
0.6mm
Projection
Extended Projection
Ground Electrode
Material
Platinum
Type
Standard
Shape
Taper Cut
Quantity
1
Specifications
Resistor
Yes
Resistor Value
5k Ohm
Heat Range
8