The QL1 is the standard lower hook for replacement on all Ortlieb Classic line of panniers-10mm. The QL2 is for the newer Ortlieb panniers. Replace one you lost or add a new attachment point to your current set up. One needed for each pannier, sold as “each.” See enlargement for QL2 hook. QL1 requires 3mm allen for adjustment; QL2 adjustment is tool-free.