There is a number stamped on the inner joints. But I can't remember what the two different numbers are. There is also a spline count difference, but you'd have to take apart the joint to see that....and I can remember the spline count either. The issue is from 14 years ago...lol.
The easiest way to tell is to just look at the axle bars. The weak ones were about 5/8" thick, while the newer ones were around 3/4" thick.
Those numbers are give or take.
If you do break an axle, it's no big deal. That does and will probably happen. It's part of the sport. Any axle from 2003-2008 will fit, so used axles are abundant. Additionally, new aftermarket heavy duty axles are fairly cheap to purchase for the 660.
Thanks dezz, I am suspecting that I will be breaking axles. I have ordered 27" executioners, shims and purple spring. When I do break one or more. Are the oem aftermarket axles stronger? Is it worth buying the heavy duty axles when I break them?
I always buy heavy duty axles if needed. Buy you have to watch what your buying. Most aftermarket companies will market their axles as "heavy duty" or stronger than original, and that just isn't the case at all.
In my opinion, the best option for axles for the Grizzly 660 is Parts Discounter Niche Axles on eBay. Simply the best bang for your buck. Those axles truly are heavy duty. I have been running them for years now, not one failure. Not even a torn boot.