public class Custom_Slab extends BlockSlab
  {
    public static final PropertyEnum<Custom_Slab.Variant> VARIANT = PropertyEnum.<Custom_Slab.Variant>create("variant", Custom_Slab.Variant.class);
    public Custom_Slab mySlab;

    public Custom_Slab(String name, Custom_Slab slabIn, float hardness, float resistance, int harvestLevel)
      {
        super(Material.ROCK);
        setUnlocalizedName(name);
        setRegistryName(name);
        setSoundType(SoundType.STONE);
        setHardness(hardness);
        setResistance(resistance);
        setHarvestLevel("pickaxe", harvestLevel);
        setCreativeTab(CreativeTabs.BUILDING_BLOCKS);
        IBlockState iblockstate = this.blockState.getBaseState();
        mySlab = slabIn;
        if (!this.isDouble())
          {
            iblockstate = iblockstate.withProperty(HALF, BlockSlab.EnumBlockHalf.BOTTOM);
          }
        this.setDefaultState(iblockstate.withProperty(VARIANT, Custom_Slab.Variant.DEFAULT));
        this.setCreativeTab(CreativeTabs.BUILDING_BLOCKS);
      }
    public Item getItemDropped(IBlockState state, Random rand, int fortune)
      {
        return Item.getItemFromBlock(mySlab);
      }
    public ItemStack getItem(World worldIn, BlockPos pos, IBlockState state)
      {
        return new ItemStack(mySlab);
      }
    public IBlockState getStateFromMeta(int meta)
      {
        IBlockState iblockstate = this.getDefaultState().withProperty(VARIANT, Custom_Slab.Variant.DEFAULT);
        if (!this.isDouble())
          {
            iblockstate = iblockstate.withProperty(HALF, (meta & 8) == 0 ? BlockSlab.EnumBlockHalf.BOTTOM : BlockSlab.EnumBlockHalf.TOP);
          }
        return iblockstate;
      }
    public int getMetaFromState(IBlockState state)
      {
        int i = 0;
        if (!this.isDouble() && state.getValue(HALF) == BlockSlab.EnumBlockHalf.TOP)
          {
            i |= 8;
          }
        return i;
      }
    protected BlockStateContainer createBlockState()
      {
        return this.isDouble() ? new BlockStateContainer(this, new IProperty[] {VARIANT}) : new BlockStateContainer(this, new IProperty[] {HALF, VARIANT});
      }
    public String getUnlocalizedName(int meta)
      {
        return super.getUnlocalizedName();
      }
    public IProperty<?> getVariantProperty()
      {
        return VARIANT;
      }
    public Comparable<?> getTypeForItem(ItemStack stack)
      {
        return Custom_Slab.Variant.DEFAULT;
      }
    public static class Double extends Custom_Slab
      {
        public Double(String name, Custom_Slab slabIn, float hardness, float resistance, int harvestLevel)
          {
            super(name, slabIn, hardness, resistance, harvestLevel);
          }
        public boolean isDouble()
          {
            return true;
          }
      }
    public static class Half extends Custom_Slab
      {
        public Half(String name, Custom_Slab slabIn, float hardness, float resistance, int harvestLevel)
          {
            super(name, slabIn, hardness, resistance, harvestLevel);
          }
        public boolean isDouble()
          {
            return false;
          }
      }
    public static enum Variant implements IStringSerializable
      {
        DEFAULT;
        public String getName()
          {
            return "default";
          }
      }
    @Override
    public boolean isDouble()
      {
        IBlockState iblockstate = this.blockState.getBaseState();
        if (this.isDouble())
          {
            return true;
          }
        else
          {
            return false;
          }
      }
  }
....
public class Init_Blocks
  {
    public static Custom_Slab endbrick_slab;
    public static Custom_Slab endbrick_double_slab;

    @SubscribeEvent
    public static void registerBlocks(RegistryEvent.Register<Block> event)
      {
    //Harvest Levels:
    //0 - Wood    1 - Stone      2 - Iron              3 - Diamond   4 - Harder than Diamond

    //Hardness Levels:
        //1 - Sign    2 - Wood       3 - Iron Ore          4 - Cobweb    5 - Block of Iron

    //Resistance Levels:
    //5 - Sign   15 - Coal Ore  30 - Block of Iron  6000 - Obsidian

        //                                                                                         Hardness Resistance HarvestLevel
        endbrick_slab = new Custom_Slab.Half("endbrick_slab", endbrick_slab,                         0.8F,     10.0F,       2);
        endbrick_double_slab = new Custom_Slab.Double("endbrick_double_slab", endbrick_double_slab,  0.8F,     10.0F,       2);
        event.getRegistry().registerAll(endbrick_slab, endbrick_double_slab);
      }
    @SubscribeEvent
    @SideOnly(Side.CLIENT)
    public static void registerModels(ModelRegistryEvent event)
      {
        registerBlocks(endbrick_slab);               registerBlocks(endbrick_double_slab);
      }
    public static void registerBlocks(Block block)
      {
        ModelLoader.setCustomModelResourceLocation(Item.getItemFromBlock(block), 0, new ModelResourceLocation(block.getRegistryName(), "inventory"));
      }
  }
....
@Mod.EventBusSubscriber
public class Common_Event_Registry
  {
    @SubscribeEvent
    public static void registerBlocks(RegistryEvent.Register<Block> event)
      {
        Init_Blocks.registerBlocks(event);
      }
  }
....
Blockstates:
endbrick_slab:
{
    "variants": {
        "half=bottom,variant=default": { "model": "megamod:half_slab_endbrick" },
        "half=top,variant=default": { "model": "megamod:upper_slab_endbrick" }
    }
}
....
endbrick_double_slab:
{
    "variants": {
        "variant=default": { "model": "end_bricks" }
    }
}
....
en_us.lang:
tile.endbrick_slab.name=Endbrick Slab
....
models\block:
half_slab_endbrick:
{
    "parent": "block/half_slab",
    "textures": {
        "bottom": "blocks/end_bricks",
        "top": "blocks/end_bricks",
        "side": "blocks/end_bricks"
    }
}
....
upper_slab_endbrick:
{
    "parent": "block/upper_slab",
    "textures": {
        "bottom": "blocks/end_bricks",
        "top": "blocks/end_bricks",
        "side": "blocks/end_bricks"
    }
}
....
models\item:
endbrick_slab:
{
    "parent": "megamod:block/half_slab_endbrick",
    "display": {
        "thirdperson": {
            "rotation": [ 10, -45, 170 ],
            "translation": [ 0, 1.5, -2.75 ],
            "scale": [ 0.375, 0.375, 0.375 ]
        }
    }
}
....
endbrick_double_slab:
{
    "parent": "block/end_bricks"
}