Sometimes, depending on what you are trying to do, you can uses them interchangeably with a little recipe modification.
Each one has different viscosity and HLB values.
Generally 20 and 80 can be easily swapped, 80 is more viscous than 20, so keep that in mind when you are formulating.
The 20, 40, 60, 80 & 85 also denote the oil it's derived from.
I can't find my notes but I think it's
20 - Coconut - liquid
40 - Palm or Tallow - liquid
60 - Palm or Tallow - paste
65 - can't remember
80 - Olive - liquid
85 - can't remember either.
Please don't take these notes as Gospel - if my info is wrong please correct me! I will search for my notes and make corrections myself if I made a mistake.
If someone know the values of tween 65 & 85, or has some good data, like a easy to read chart on all I would love to read it.