The part number for a 56 series plug to go with 56C550 is -
56P550 (Australia) or PDL56P550 (New Zealand)
Please go to the website via the following links below and check under the Documentation Tab for more information.
Australia - https://www.clipsal.com/products/detail?CatNo=56P550&itemno=56P550-EO&backto=/search?q&tab-document-1=0
New Zealand - https://www.pdl.co.nz/products/detail?CatNo=PDL56P550&itemno=PDL56P550&backto=/search?q=56P550&tab-document-1=0