Still have no idea which bolts to use but for anyone interested in these black modular steel wheels with offset ET34 here's some pics and info.
My van came with 20" Navis Ludis 9" alloys. Looked great but the drive was too harsh and I was always scared of kerbing them or meeting a pothole. Also I wild camp so go offroad sometimes but I didn't want Al Terrains so I went for 17" steels with Michelin All Season tyres. This gives me an all round tyre and lots of it, so potholes don't scare me any more.
I bought the tyres, wheels and bolts from eBay seller Tyres Direct On-Line. They looked fine but the VW centre caps didn't fit. They just fell right off. After much head scratching I worked out that the bolts on had 17mm heads and that VW ones had 19mm heads. The VW ones also had a groove in them that the clips on the centre caps latched into. I rang WheelPartsDirect.com to make sure I got exactly the right bolts. When they turned up they looked nothing like the bolts that had come with the wheels but instead looked just like the bolts that came with an original VW 17" alloy wheel I have for spare.
So I suspect that they sent me the wrong ones. I'll find out on Monday. Meanwhile I am beginning to doubt that there is such a thing as a VW bolt for steel wheels complete with 19mm head and groove that the VW centre caps will fit to. If anyone can ease my troubled mind by posting a photo of one I'd be very appreciative.
Meanwhile here's some photos...
Bolt on left supplied with 17" modular steel wheels, bolt on right supplied by WheelPartsDirect.com
Bolts in the wheels...
Bolts supplied by WheelPartsDirect.com supporting the centre cap (note that cap stands proud of wheel. I've no idea if it's supposed to do this).
And for anyone who may be interested this is how the wheels and tyres look on the T32 (lowered by 70mm on Bilstein NSLs)....
Thanks