What thickness lifting belt should I buy — 10mm or 13mm?

Reddit powerlifting threads in the signals repeatedly note that 13mm belts are extremely rigid but can dig into the ribs and gut, especially on deadlifts, and several lifters say they wished they'd bought 10mm instead. The general consensus is 10mm is the most versatile thickness for most lifters, with 13mm reserved for advanced powerlifters who specifically want maximum stiffness.