Yes they are M6 (just checked with a known M6 nut).
I measured one spike. The threaded part is 20mm long. The straight part is 11-12mm long. The pointy bit tapers over 14-15mm. I guess the rest are mostly the same within engineering tolerences and certainly beyond my measuring skills.
Does help What's the dimension, flat to flat, on the M6 nut? Just so I can make sure it's M6 spikes I need. If so I'll take them at £12 posted if Loud & Clear don't have my spikes by tomorrow/wednesday.