The Wall Spacer pack is part of the Castle Builder System. It is made of "Dwarvenite" and includes some metal and magnetized parts. This item was initially available as an add-on to a pledge level during the Castle Builder System Kickstarter. It was not advertised during the Kickstarter campaign but was made available during the final order. The item comes in both painted and unpainted versions.
The Wall Spacers pack comes with these 4 pieces:
(4) Wall Spacer