Scooterotica

Hi all. My Series 2 has the earlier "W" shaped folded metal horn bracket (not the later single stud). The current horn is a non-standard one with a single fixing tab, fixed with a self-tapper. Obviously the original fitment was a horn with two fixing tabs, but what fixings were used?: the thumbscrews I've seen on-line for fixing horns on Series 3's tend to be M5, while the holes in the horn bracket on my Series 2 seem to be M4. Also were rubber grommets used for fixing early Series 2 horns? I've had a good look for images of the arrangement on-line (or so I told the missus ...), but can't find anything clear. Many thanks in advance