I confirm what the user above me said, they were T8, at least on my Xbox.
As the user above me said, please avoid doing it like shown in the guide. It just didn’t work on my Xbox (unless your goal is to destroy the plastic case). Instead, pick some small needle like object (the spudger was too short for this, I used the SIM bit of my iFixit driver kit) and find the right spot on the big sticker which is on the left in the pictures shown in the guide. That spot is just between the text and the column of logos (Dolby Digital, etc.) (https://team-xecuter.com/slim/slim_secre..., picture not mine). Poke it (don’t be too gentle, you have to apply some force) and you will hear the clip release.