I have a Deere 310C Likely 1989 vintage... I also have a good collection of sockets in 1/2 inch drive. :notworthy For the larger sizes, I'm looking at 3/4 drive. Which socket set will have more use on the 310C ... Metric or SAE? Or should I go to 1" drive sizes ...
Go buy a digital caliper, one that has metric and SAE scales and start measuring the bolts and nuts on your beast. HF Freight is more than good enough, you don't have to get Mitutoyo or Starrett. Then you can see what's needed. 1" drive is really expensive compared to 3/4", so I'd go with the smaller one. The few sockets you'd need in 1", buy just those on Ebay, used.
Look at this http://www.4x4wire.com/tech/screws/Grade_Class_Properties_Identification.jpg You can tell from the markings on the head if the bolts are metric or SAE. I have 2 complete 3/4 drive sets, one SAE and one metric (I work on stuff a lot bigger than a 310) Lots of sockets will cross over, or be close enough that you can get by with the SAE. I hardly ever take out the metric kit. Most of the time I am using a 3/4 impact so I am running 3/4 drive, 6 point sockets. So for instance, I use a 1-1/16 socket for a 27MM, 1-3/16 for 30MM, 1-7/16 for 36MM. The fit is pretty good. If the nut is badly rusted or corroded you might need the proper socket, but I would say most of the time I get by with SAE no problem. My big combination wrench set goes up to 2". I don't own a metric combi larger then 27MM Not all sets will have all of the sizes you need so something to watch for. My metric 3/4 set is a cheap made in china $99 special. The ratchet was crap but every thing else has been good. My SAE is SnapOn. Worth WAY more then $99 bucks but have had it for close to 40 years and have never even put a kit in the ratchet My 3/4 impact sockets are all semi cheap Chinese (Jet and Westward, don't know if you have those in the states). I can wear them out pretty quick on a job like track pads, or I lose them in the mud, that's why I go cheap on them. Hope this helps