Your spacer will be made of Red Eucalyptus. Eucalyptus macrorhyncha, commonly known as red Eucalyptus or red gum or red stringybark is a small to medium-sized tree with rough, thick fibrous and stringy, dark-brown bark. E. macrorhyncha was first recognised as a distinct species and given its name by Ferdinand von Mueller. In 1867, George Bentham published a formal description in Volume 3 of his Flora Australiensis. Bentham's description was based on syntypes collected by Mueller and Frederick Adamson.