How to set a Blockhitbox to a Customblock (JSON)

is this what you are looking for?

@Override
		public VoxelShape getShape(BlockState state, IBlockReader world, BlockPos pos, ISelectionContext context) {
			switch ((Direction) state.get(FACING)) {
				case UP :
				case DOWN :
				case SOUTH :
				default :
					return VoxelShapes.create(1D, 0D, 1D, 0D, 1.8D, 0D);
				case NORTH :
					return VoxelShapes.create(0D, 0D, 0D, 1D, 1.8D, 1D);
				case WEST :
					return VoxelShapes.create(0D, 0D, 1D, 1D, 1.8D, 0D);
				case EAST :
					return VoxelShapes.create(1D, 0D, 0D, 0D, 1.8D, 1D);
			}
		}

good for you

Hi Sasky i know this toppic is a bit old but can you say me how do you set hitbox as costume json?