Having a Hashed version of the primary key can speed up lookups from other tables, especially if the primary key consists of multiple alphanumerical fields.
1. Right click the table → Advanced → Advanced Settings
2. Check the box for Enable BK Hash Key .
When that option is checked, the Jet Data Manager will generate a Hashed version of the Primary key fields(s) using the SHA1 Hashing Method. If no primary key is selected, then the BK_HASH_KEY will contain a hashed version of the DW_ID Field.