The thickness of the oil is officially rated in Centi Poise "Cps".
Another known and used American rating is WEIGHT "WT".
This WT or W rating is a non world standard and was introduced by Associated and not comparable between brands using this W or WT rating.
Concerning Cps the thinner the oil (fluid) the lower the number, the ticker the oil the higher the number.
For normal shock absorber use, this rate may vary between 100 Cps up to 900 Cps.
For diffs the rate may vary between 1.000 Cps (loose) up to even 500.000 Cps (very, very, stiff).
USA based companies use the "WT" weight rating, where Japanese and European companies use the better linear industry standard Centi Poise rating.
A lot off people think that the ratings between the "WT" and "Cps" ratings are linear but this isn't the case.
You can find the whole story and charts here: