What would be the business code for selling T-shirts on websites like Teespring?

[TomK]

Business codes are used by the IRS to categorize your business for statistical purposes only. The code you enter will not affect the outcome of your tax return.

When your set up your business in TurboTax, you'll eventually come to the Enter Your Business Code screen.

Simply click the Lookup Business Codes button, enter some keywords that describe your business (e.g., day care, bookkeeping, door-to-door, etc.), and then click Search.

Select the code that most closely resembles your business's activities. If you can't find a code that applies, you can enter 999999.

You have a number of business codes to choose from (see link below - pages 17 - 18): https://www.irs.gov/pub/irs-pdf/i1040sc.pdf

For example:
448140 Family clothing stores

453220 Gift, novelty, & souvenir stores