Polyurethane -- I always lube with silver anti-seize, for just about any application, where it meets metal. That's what I did for red poly cush drive pucks also.
Note that the cush drive I have uses different pitch thread than the stock... so watch for that when buying aftermarket aluminum or titanium hardware.
I noticed that the Allen / Hex head on the back of the inserts was a standard not a metric...
But the instructions say you can use the stock nuts. And they did fit on my dry fit.
The email in my previous post is from where I purchased the inserts.
On the marketing they are suppose to expand this is why I questioned the application of grease, not to mention they were very tight.
I washed the grease off that I had applied to the carrier and inserts. Soaked the carrier in hot water, while the inserts were in a bag in the freezer for a few minutes. Towel dried the carrier then installed the inserts. They went in very easy.
I'll report back on the wear in 10k miles or sooner.
Thanks everyone