Ohhh something I can be of use with, got two of these kits for crimbo

These are the kits that are £6 from oddballs right?
The nut included with the kits has a thread that's too wide for the sundia bolt. You need to push the nut included with the kit out and replace it with the original nuts from your sundia. The white part you're talking about is solid, you cant do anything about it.
In my case a couple of the nuts just fell out when I pulled them out of the packets. The other two, I had to push out from the plastic side (underneath the bolt) with a thin screwdriver. Once all the nuts are removed you can attach them.
I'm not certain on it but I don't think you can use the metal/carbon washers with the light kits on unless you find a bolt a few millimetres longer. I took off the washers and left the ting serrated washers over the bolt then attached the light kit and finally the original sundia nut.
Lovely kits, super bright but there are issues with the switches. On some of mine, the switches stick out enough to switch on and off easily but on one of them, the switch needs a pin for me to reach it, not the end of the world but a bit of a pain nonetheless.
Half the price of finesse and sundia kits though and doing well so far, rainbow coloured and like I said nice and bright.