I learnt the hard way as when I replaced my brakes I didn't know about this tool and had to resort to calling her indoors to come and put her foot on the brake so I could put the bloody wheel on without the disc moving! Still didn't stop the hub from rotating
Once I found that there was a tool in the tool tray I went out to check but as it happens, it was broke!
Would not have this problem if Audi would just use disc screws
bought one from eBay, I think it's a draper brand!