I had to box up some old tubulars to ship to
rancho66 today. I've been using Pirate Ship for a while now (USPS and UPS) for a couple reasons. In addition to Priority Mail/Express service, they quote First Class and Parcel Select, making comparison shopping a bit easier and saving a trip to the post office.
I entered the package dimensions and weight and lo and behold, a new Priority Mail service popped up, Priority Mail Cubic. I'd never heard of it before. I wasn't sure what USPS boxes I could use, so I asked. I could use my own box or any USPS packaging not marked flat rate or regional rate. I had already boxed up the tires in a Regional Rate A box, so I just went with that option.
The person I was chatting with said Priority Mail Cubic isn't a new service, but it's reserved for shippers who send at least 50,000 packages per year. Pirate Ship qualifies, so they decided to make it available to their customers. They have an explainer on their website:
https://support.pirateship.com/en/ar...ity-mail-cubic