Letterlocking Category: Fold + Mechanical Lock
DB-1299. Red string secures this multi-page letter shut after it was folded in quarters. The string is tied in a knot and is the "mechanical lock" . There is no adhesive used in this category of letterlocking formats.
Letterlocking: Brienne Postal Archive: A long letter folded, tied, and placed in a wrapper
Fold + Mechanical Lock-N
One of the letterlocking format categories includes any object that is folded and secured with a mechanical lock. Often, the mechanical lock is removed and discarded.