Thanks for trying Booboo. And unfortunately for me, but fortunately for Chas, he is away for a month(actually he has told me that he doesn't have any of these items). In the meantine I have been through the catalogue of the main plastic parts manufacturer and they have no rectangular captive nuts small enough to fit the 12x8mm holes. I also tried a stockist of old car body fixings with no luck. Rawlplug type fixings won't work;I have tried several types. Spire fittings may work but will cause my newly painted chassis to rust where the teeth dig in through the powder coating.So, I am stuck unless I resort to making a couple of wooden inserts.