Part number of the extension ring to suit 240 series junction boxes are
249/12 or
249/25. Extension Rings fit all 240 Series Junction Boxes and are designed to provide extra space for additional terminations or bring forward the fixing points to allow easier mounting of accessories.



Please go to the following links below and check under the Documentation Tab for more information.
Australia
https://www.clipsal.com/products/detail?CatNo=249/12&itemno=249/12-GY&backto=/search?q=249/12&tab-document-1=0
https://www.clipsal.com/products/detail?CatNo=249/25&itemno=249/25-GY&backto=/search?q=249/12&tab-document-1=0
New Zealand
https://www.pdl.co.nz/products/detail?CatNo=249/12&itemno=249/12-GY&backto=/search?q&tab-document-1=0
https://www.pdl.co.nz/products/detail?CatNo=249/25&itemno=249/25-GY&backto=/search?q&tab-document-1=0