Pirate Ship currently offers 4x6" and 2x7" label sizes. And in order to use iDPRT thermal label printer SP410 or SP420 in Pirate Ship, please select the 4x6” label format, and head to your Settings > General Settings:

Keep in mind that you must set your label size before you create any labels. The size you select will apply to all label purchases going forward, and you will always need to head back to your Settings to make any changes!

Reference from:

Reference from: https://support.pirateship.com/en/articles/4140701-how-can-i-change-the-size-of-my-label