USPS changed their software interface, and now their shipping options aren't showing up in our check out process. If you're ordering a small part and it qualifies for USPS first class, choose UPS Ground and we'll refund the difference to your credit card. All you need to do is drop a note in the "customer instructions" when placing the order.
If you want Priority Mail, choose UPS Ground and drop a note in "customer instructions" for your shipping choice. UPS Ground and Priority Mail are around the same price for domestic shipping, so there would be no refund on Priority Mail. We're working to get this fixed ASAP, so bear with us.