If you want to build a Part, you will need a Part Builder!
Doesn't sound that hard, does it?

It might be required for you to import the package if you encounter any issues, so better be safe than sorry and add the import.
import mods.contenttweaker.PartBuilder;

You can retrieve a new, clear Builder using the MaterialSystem Package:

ZenScript
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var pBuilder = mods.contenttweaker.MaterialSystem.getPartBuilder();

You can set these Properties

ZenMethod	Параметр
ZenMethod setHasOverlay(hasOverlay)	Параметр boolean hasOverlay
ZenMethod setName(name)	Параметр string name
ZenMethod setPartType(partType)	Параметр PartType partType
ZenMethod setOreDictName(prefix)	Параметр string prefix
ZenMethod setAdditionalOreDictNames(prefixes)	Параметр string... prefixes

All these Methods do 2 things: Firstly, they change the builder's Property, secondly they return the modified builder.
You can see in the example scripts below what this means.

Before you can build your material, you need to build it:

ZenScript
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pBuilder.build();

This returns an Part Object.

ZenScript
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var pBuilder = mods.contenttweaker.MaterialSystem.getPartBuilder();
pBuilder.setName("dense_gear");
pBuilder.setPartType(MaterialSystem.getPartType("item"));
var denseGearPart = pBuilder.build();

var denseIngotPart = mods.contenttweaker.MaterialSystem.getPartBuilder().setName("dense_ingot").setPartType(mods.contenttweaker.MaterialSystem.getPartType("item")).setOreDictName("superIngot").build();

The items you create with your new part will generally be named contenttweaker.part.partname
If you want your item to include the material name, you will need to localize it, preferably in CoT's language files which can be found at Resources/contenttweaker/lang.
Instead of the material name you write %s, so naming the dense gears ans ingots created above would look like this:

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contenttweaker.part.dense_gear=Dense %s Gear
contenttweaker.part.dense_ingot=Dense %s Ingot

The items you create with your new part will look a bit edgy to you.
If you want your part to have a specific icon you will need to add a partname.png file to Resources/contenttweaker/textures/items.
So, giving the dense gears a texture would require us to add a file called gear_dense.png to that folder.