Some of Fredo's extensions have become 'paid'.
The perpetual licenses are not costly.
Clicking on one of the buttons on the dialog you showed will take you to a page with more info, and where you can buy licenses using PayPal...

It looks like you are running up against the tiny face limitation in SketchUp. Instead of trying to draw it at 6mm in diameter, set units to meters and draw it so it is 6m in diameter. Then scale the model down after you are finished.

These are 4mm bolts which I modeled that way.
Screenshot - 7_11_2020 , 12_35_18 PM.png

These are 6mm shoulder screws also modeled with the same method.

https://live.staticflickr.com/65535/49627196177_7d2ae945ef.jpg

@Pilou - well spotted - it's a well known typo disaster in English - NOB v. NOW - which reverses the meaning...

I corrected the original, FTAOD...