I tested mine once with a socket just to make sure it could be done. I got a handle with mine, so I didn't NEED to use a socket, but I wanted to know I had a redundant manual solution. I don't recall what the size was, but JFlightRisk sounds right at 3/4".
It may be a moot point anyway; if yours is anything like mine was, it will fail soon anyway. Then you can get a good quality jack and not have to worry so much about the manual override.
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!