If servicing Spartan seacocks you'll need two 15/16" wrenches or a 15/16" wrench and a smaller 3/4" wrench for the smaller size jam nuts on the 3/4" valves.
It's important to note that you will need a thin "spanner" type wrench as the flange nut is thinner than most 15/16" wrenches. The Wilcox Crittenden valves will take a full thickness 15/16" wrench on the flange nut but the Spartans will not.
What I did is simply grind down a Harbor Freight quality 15/16" wrench on my bench grinder to fit the Spartan flange nut. If your wrench is to thick you won't be able to effectively "lock" the two nuts together and they may work loose.
If you click on this picture, to make it larger, you can see where I ground this wrench thinner to fit the jam nut. This took about 5 minutes on a bench grinder and I think I paid about $3.00 for the wrench.