The codes split by market and drivetrain. BB6 is the most common USDM code (base model), and BB8 covers the SH trim in North America. BB5 and BB7 are JDM and other-market designations with different engine and trim combos. Structurally, the unibody is the same across all four codes. The meaningful differences are engine tune, ATTS vs. open diff, and interior/exterior trim pieces. If you're sourcing parts, most suspension, brake, and body components interchange across all BB codes without modification.