I know it’s been over a month, but I wanted to say that this is pretty helpful! After Roblox announced (then postponed) a terrible update that would mess up the platform as a whole, I started considering making my own body part bundles (for use in my own experience only, so those policy changes wouldn’t apply to me).
A few hours ago, I applied the clothing template textures to a character (with shading so I knew which sections were used by bottom faces of parts), then exported it as a model, which gave me a color-coded texture of what I like to call the “internal classic clothing UV layout”.
I was unsure about what the boxes with four colored triangles were for (for the limbs), and your post explained each one’s use well!
If I do challenge myself to make a custom R15 body, the information here will help me, when used alongside this texture.
Reading the post that you linked to, I now know that my “texture” here isn’t the one used for UV mapping; Individual parts use a smaller texture, which in turn becomes part of the “composite” texture. (Why did Roblox make classic clothing UV maps so complicated?)
