Glossary
UsrClass.dat
The per-user classes registry hive that holds most ShellBags on Windows Vista and later, stored in the AppData Local folder of each profile.
UsrClass.dat is the per-user classes hive, at C:\Users\<user>\AppData\Local\Microsoft\Windows\UsrClass.dat. Windows mounts it at HKEY_USERS\<SID>_Classes and merges it into HKCU\Software\Classes. Its root key name carries the user's SID.
Since Vista, the main ShellBags tree is in this hive, under Local Settings\Software\Microsoft\Windows\Shell\BagMRU. It is locked while the user is logged on: collect it raw with its .LOG1/.LOG2 files. See where ShellBags are stored and how to collect them.