While I have the full list, showing it here would be spoilers till later on, so I'll cut it down and show the more relevant grades for this part of the book.
Skill Ranks
Unskilled – 1-10
Apprentice – 10-20
Adept – 20-30
Professional – 30-40
Expert – 40-50
The 'item grades' are as follows, the number following represents the skill used to complete it
Crude <15
Common 16-25
Uncommon 26-40
Rare 41-50
Very rare 51-60
The skill ranks were designed in such a way to eliminate some randomness for dice rolls in tabletop games, this means it is very rare for a persons 'overall work' to dip outside of their skill range.
To get an overall idea of how a task is calculated, you take the skill number you have currently, lets give my gaming skill a [24].
If I wanted to perform higher than my current skill level, I can. The same goes for if I'm having a bad day and I play worse. This is the 'range of possibility', usually a +5/-5 of the skill level.
This means with my skill of a 24, the worst I can play if I'm trying hard is a 19. Which will let me beat anyone who has a skill of 14 or lower because the highest they can get on a good day is 19 (14+5=19).
This allows for a degree of randomness in design, but also gets rid of the key point I dislike in D&D and other tabletop games.
In D&D your amount of skill doesn't matter even if you have high bonuses, someone without a bonus can do better than you, even if they don't know what they are doing, and you did it all your characters life. They could be entirely new to the task and complete it based on luck, vs a person who spent tens of years in game training at that skill..
I won't roll a 5 and get my bonus of a +5, getting beaten by a total amateur because of 'luck'. Instead in the system I've been working on, I still have a high chance of beating people who are a few points behind me.
Tl;dr, a person 5 points behind another, it becomes impossible without special tools or the support of others; to create or do something better than that person 5 points above.
Because it does matter for the whole style I'll be using, yes there are skills and those will be the core training characters do, while these 'grades' tell you how good they are at doing things, the skills are the applications of these points.
Things like skills and teachings people pick up enhance their power with completing a task. In the case of a sword skill it is the difference between putting your strength behind an attack, or knowing how to deflect that attack to defeat the opponent. While someone with brute strength can quickly improve, they are no match for someone at the same level who holds teachings towards that skill.