Nuts aren't measured in "wrench" sizes but the thread size. The threads on Ed's ball joints are M12x1.5 - or "M12 fine". If you have just bought a normal M12 nut then it will be M12x1.75 so won't fit. Looking at the "Megapack" website though it says their nuts are M12x1.25 - which is called "M12 Extra Fine". You need M12x1.5 ......
All of the originals and the replacements from us use "UNF" thread (not metric)
If you put the club upper ball joints in instead, it will be ok as long as there is enough thread to tighten the nut. So you would first measure the length of the threaded bit (18mm), then install the joint. Once it is installed and tight, measure from the end of the shaft to the bottom of the nut. If this is 17.5mm or less then you are ok
- if not then you will need to use a 1/2" washer to space it out, but just check the washer is central, and NOT stainless. I have 1000 of these in stock and can provide you with 2, no problem.