I think you'd have to be lucky for the mechanic to have the right socket, Deejay. I just took a look - normally deep-format impact sockets step down to around 70% of the hex-size, less than an inch back from the end of the socket. This job requires it to stay up to about 100% of hex-size, because of the ratchet wheel on top of that dog-nut. I think you'd have to find a thick-walled tube-type spanner (one that is fully forged, not one made from tube). They exist - I seem to have one or two, but they are older than I am, and in Whitworth sizes. This looks like a case where you have to go to a serious tool shop and buy a suitable spanner, or laboriously bore a deep impact socket to clear the ratchet wheel, or make do with the thickest-walled ring spanner you can find. I notice that the old Australian-made Sidchrome rings were pretty stout by the time you got up to that size.
