Grinders use the Balance part of any weapon or item to grind with. This means that if you gave a green fragtrap classmod the balance of a legendary rocket launcher, the grinder would interpret that class mod as a legendary rocket launcher.

I have created a bunch of characters full of Eridian Vanquisher Lawbringer class mods that have balances designed for perfect grinding.
(See; https://www. mediafire. com/ folder/ 85i9221m9ado9/ Matchmakers)

These class mods have the balance of legendary items and weapons from different categories, each category is indicated by a rarity on the class mod:

Class (Legendary) BLOZ(CgAAAACSkgALDhLg4zCBxwzAEUAQwP///////////z8SQApCAMA=)
Weapon (Purple) BLOZ(CgAAAAALkAALDiqA4zCBxxPAEUAQwP///////////z8SQApCAMA=)
Shield (Blue) BLOZ(CgAAAADeLwALDkyI4zCBxwrAEUAQwP///////////z8SQApCAMA=)
Grenade (Green) BLOZ(CgAAAAChtAALDgJY4TCBBwzAEUAQwP///////////z8SQApCAMA=)
Oz Kit (White) BLOZ(CgAAAACzUwALDtB44TCBBwDAEUAQwP///////////z8SQApCAMA=)

3 'Weapon' = Random Legendary Weapon
2 'Weapon' + Purple(Type) = Legendary(Type)
3 'Shield' = Random Legendary Shield
3 'Grenade' = Random Legendary Grenade
3 'Oz Kit' = Random Legendary Oz Kit

Known Rarities: [In order of rarity]
{Glitch}
Ultra_White [>9]
Ultra_Legendary [9]
Pale [8]
Mint [7]
Ultra_Purple [6]
AG_White [5]
Glitch [4]
Pearlescent [3]
Gold [~:2]
{Regular}
Black [>11]
AL_White [11]
Legendary [7:10]
Etech [6]
BE_Legendary [5]
Purple [4]
Blue [3]
Green [2]
White [1]
Grey [~]

Numbers contained within [ and ] are points, these points are a logistic construct I have developed to explain where rarities exist, I have used these points to figure out different ways to create these rarities. Also '~' means '0' and below.

Three parts make a difference to the rarity of a weapon:
~ Body
~ Barrel
~ Accessory 2

Body:
Each body level adds more points:
No Body = 0
Body with no following = 1
Body A or 3 = 2
Body B or 4 = 3
Body C or 5 = 4

Barrel:
Legendary barrels will increase the rarity by 5 points.

Accessory 2
Whenever a weapon has a Glitch accessory, it will have an entirely different set of rarities.

This section will define what each part in a class mod does. It will not focus soley on rarity.
Parts in question:
~ Type
~ Alpha
~ Beta, Gamma, and Material

Type:
Type gives 5 points if legendary.

Alpha:
This is the specialisation base type. It defines the base rarity of the class mod
The number next to each part of the skill adds skill points based on the SX values.

X=1, 2, or 3;
Spec_Legendary = 8 (Legendary)
Spec_ASX_(-)BSX_(-)CSX = 4 (Purple)
Spec_ASX_BSX = 3 (Blue)
Spec_ASX = 2 (Green)
Spec_NoSkill = 1 (White)
No Alpha = 0

Purple: A = +2, B = +1, C = +0
Blue: A = +3, B = +2

Therefore Etech is Blue + Blue (Tested and proven)

Beta, Gamma, and Material
This adds to the attributes on the class mod. (E.g. Shield recharge delay)
X=0,1,2,3,4, or 5
Beta: PrimaryStat_AX_B0_C0
Gamma: PrimaryStat02_A0_BX_C0
Material: StatPenalty_A0_B0_CX

A is the first attribute, B is the second attribute, C is a penalty to both

Parts that influence rarity:
~ Delta
~ Material

Delta:
Deltas are the special effects of shields. Legendary accessories will increase the rarity by 4 points.

Some shields will use the Balance instead of Delta for the extra points required to reach BE_Legendary and not Legendary (hence why some legendary shields are BE_Legendary and some are Legendary)

Material:
The Material is what influences the stats and rarity the most out of any part of the shield (by a significant factor).
Rarity Increases:
No Material = 0
Uncommon = 1
Common = 2
Rare = 3
VeryRare = 4
Legendary = 5

Note: Either the material alone and not the delta will be responsible for most legendary shields as they are usually BE_Legendary and not true Legendary (5 + 4 = Legendary, 5 + 0 = BE_Legendary)
True legendary shields will have both 4 points from delta and 5 from material.

Parts that influence rarity:
~ Type
~ Epsilon

Type:
Legendary Types increase rarity by 5.

Epsilon:
This is the damage part, it will dictate the rarity of the grenade.
No Epsilon = 0
1 or 2 = 1
2 or 3 = 2
4 or 5 = 3
6 or 7 = 4

Parts that influence rarity:
~ Eta
~ Theta

Eta:
Legendary Eta adds 5 points

Theta:
No Theta = 0
Theta 1-3 = 1
Theta 4-7 = 2
Theta 8-11 = 3
Theta 12-15 = 4