So this is the second clip on mirror of this type that I have bought. I needed a mirror for my old Lotus Seven but was slightly concerned that it might not fit especially with the stated 3mm maximum thickness for gutter attachment. I found that if prepared to remove the rubber/steel packing pieces (there to protect paintwork?) I could mount onto the screen stanchion with ease, just slightly marking the aluminium with the grub screws. Also I was able to bend and adjust the mounting bracket to a more favourable angle for my application ( should also fit Caterham 7s with the same windscreen stanchions).
So after a good result for the drivers side I've now bought and fitted a second for the nearside!

Nice product easily fitted.

Très bon rétroviseur pour ma westfield seven