I have an object that has 2 CASTable parts, but it also has screws in it which i want to always remain looking like a screw texture and to not be included in the part mask as colour/material changeable. I'm sure i may have come across this before but i cant seem to find anything on it now =/ .. Is is possible, and if how do you do it? Which image file is it to do with? I hope i've been clear with what i mean!

I know that plants have some non-CASTable parts. perhaps you can clone your objects from a plant? for a plant there is a separate dds file for this parts. I don't know if you can add such a dds file for other objects.

Ah thanks for that, might have a look into that! Thing is that my object is for on walls, so i originally have cloned it from a light.. If i clone it from a plant is there a way to change the behaviour to that of a light - ie. snap to walls? Come to think of it i wonder if the wall-hanging plants have that non-castable part.. that would be perfect. Will look into it, thanks!!

On which image file (specular, greyscale etc) would i put the actual screw texture i wanted to make default though? Although after just cloning the hanging wall plant it looks like that objects going to work, will redo my object using that and see what happens

I agree with Killc*a about plants. In plants, you would paint black in the greyscale's alpha where the screws are. Put the screw texture on the dds Killc*a mentioned and white in its alpha where the screws are (opposite of the greyscale).

EDIT: The black on the greyscale alpha is only needed for transparent areas like cut outs for leaves on plants (not needed for your screws, sorry).