einhell petol strimmer

got a einhell petrol strimmer einhell BGBC 25AS need to get spark plug out but none of my spark plug sockets fit, i messed around and found a 19mm ordinary sock fit it but its too shallow, is 19 mm the right size i require plz? before i try and buy one

 

thank you very much for your reply and thanks for list of equivalents for plug,