Since this is the only part I know anything about I’ll answer this. The SD cards are all 3.3V as far as I know so assuming your Mega is running at 5V the chip is likely a 74ahc125 (I made a Friting part for this that is available in parts submit). The 74ahc125 with VCC at 3.3V will tolerate 5V from the Mega on its input pins (unlike the SD card) and output the signal at 3.3V to the SD card. Putting 5V in to the SD card may damage the card.
Peter