A borrowed $5 or ring is threaded onto the shackle of a lock, then the lock is snapped shut.
Everything is placed in the spectator's hand or covered with a handkerchief.
Performer takes a $1 bill from his pocket. Instantly shows the $1 & folds it up and close his fist. Immediately the items to change (transport) locations!
Now the magi is holding the borrowed $5 and locked on the lock shaft is the magi's $1!