This may be a silly question, but I'd like a second opinion before I go purchasing the wrong tool. I'll be changing both Tides shaft seal kits (the whole assembly) during our upcoming haulout and am getting parts and tools gathered now. They are original to the boat (2002) and are in poor condition overall.

Based on the attached drawings, it looks like the nut (Item 7) that holds the coupler on the shaft is a 2 1/4" nut, but I just want to make sure I'm reading it correctly. If you look at all the other items, they use the "inch marks" with the dimensions, but not on this part for some reason.

I've also heard that it is a nyloc nut and requires a thin-wall socket to fit inside the coupler. I wasn't sure what all the nomenclature for "CSL 2-1/4 SHT" meant.

Has anyone done this job and/or have any other advice? Thanks in advance!