Just my 2 cents... Typically, one uses a washer(s) between a nut and a sprocket. Especially when the surfaces of the nut and sprocket aren't totally smooth (like a mirror). Washers allow slight rotational vibration of the sprocket without loosening the nut. That's the theory anyway... Here are some pics (this is the first time I've tried uploading any pics here)...
Here's the axle in place...
Here's the 1st washer between the axle spacers and the sprocket...
Here's the Sprocket/Pulley in place...
I used a pair of SS washers (concentric) between the sprocket and axle nut...
Used some Loctite 641 retaining compound on the axle nut and torqued it to 250 ft/lbs. Then installed a CycleSprings "lock" on the nut. It hasn't moved to far -- but I'm still crossing my fingers...
I had no idea why Polaris didn't use washers in the first place -- until I tried to find washers the right size... Yeah, a squirt of Loctite is a lot cheaper!