There are two models: padded and not padded.

Here is an example for a padded strap: https://www.etsy.com/de/listing/732386622/bs63-leder-gitarrengurt-lederriemen-fur

This is a top shelf non-padded strap:

https://www.gear4music.com/Guitar-and-Bass/Fender-Artisan-Crafted-Leather-Guitar-Strap-25-Brown/1IWD

Padded straps are a blessing when you have a heavy electric guitar, for acoustic guitars a simple leather strap will do. Having a wide strap is always nice.

2mm?

More important are the holes. They got to be stiff but can't be to thick, otherwise the thingy on the guitar slips out: