Frying pan hole: the other option is to permanently glue something inside the hole. I'm betting he'd fit in it, that's why I'm concerned. Always remember snakes are NOT logical about fitting all the way thru things- plenty are killed that way, when they get stuck & cannot back out because their directional scales prevent them from doing so- they "catch" on whatever the snake is stuck in.
And you can never trust pet stores NOT to sell you things that look 'cool' but are dangerous for at least some pets, like those "fake skulls" with many holes where some snakes can get stuck.
You might ask the seller for an estimate of the snake's length- to give you a better idea of his head size & all. While you're asking about the size of air holes...
I love tiny snakes & they do grow, eventually, but you have to be prepared for the differences in housing them. I have lots of practice with tiny snakes- I've raised plenty of corn snakes etc., whose heads are about the size of a sunflower seed. Remember that snakes are soft enough to smoosh their way into holes, especially air holes with enticing odors "elsewhere" in the room- they just like to explore, which is why they're fun to watch. But we have to do their thinking for them, lol.