the photo looks like the nuts are hard plastic.
If they are not loaded, plastic might be a better choice as it would reduce the vibrating loose, just need to watch the torque at installation
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.