I decided to swap out my SP140 swing arm bolts with something with a little more meat on it:
Now, the original bolts seem like they are good grade 12 bolts, so they should be fine.
The replacement ones I picked up have a lot more shoulder and are designed for that shoulder to have things rotate on it so it should be pretty perfect for this. They are a little bit shorter than the provided bolts but do thread all of the way into the nylon lock nuts. If I ordered again I’d probably get the ones that are 5mm longer and some lubricant filled nylon washers. Here’s where I ordered them in case you want to pick some up for yourself: Same-Size Thread Alloy Steel Shoulder Screw but seeing the price of $6.50/each suddenly makes it clear why these aren’t the default.
If any of you have the Iris quick release hub, I also grabbed these bolts: Black-Oxide Alloy Steel Hex Drive Flat Head Screw to replace the ones that were included with the hub because the ones with the hub are just barely too long and will bind up on the motor.