Other Stromtroopers confirm the measurement
The nut requires a 32mm socket.
Harbor Freight sells a set of half-inch sockets, the largest of which is the required 32mm. It might be cheaper to buy one socket (which HF does not apparently sell alone), but I found it expedient to get the set, at a time when it was on sale. I have since used another socket in the set, so I reckon I was right to get them all.
Maybe the shaft is 20mm in diameter. Search on "Sprocket socket" and you will find tales of hard work to remove stuck nuts, along with advice from much more talented wrench-turners than I am. If your nut is stuck tight, you may benefit from the wisdom you'll find there.
Not on topic, but I went from a 15-tooth front sprocket to a 16-tooth on my Wee-Strom, and I like the taller gearing. Next time I change sprockets, I will get even more teeth up front or fewer out back, because even taller gearing would suit me better. I don't yank out a lotta stumps, ya see. 16/47 lets me accelerate uphill in sixth with 170-pound me and a 260-pound passenger and 30 pounds of gear.