Abstract: A tape transport mechanism 10 includes a base member 12 which defines a slot 24. A plate 14 carrying recording and/or playback heads 15 thereon is slidably mounted on the base member 12 over the slot 24. The mechanism 10 includes a substantially wedge-shaped displacement means 16 pivotally mounted within the slot 24. The displacement means carries a pair of rollers 22.1, 22.2, and is pivotal through a predetermined arc of travel by means of a motor and gearbox combination 28. The rollers 22.1 and 22.2 are engageable with spigot formations 44 which project from extensions 42.1, 42.2 extending from the plate 14 into the slot 24. When the plate 14 is in its operative position in which the heads 15 engage a cassette tape, the spigot formation 44 of the extension 42.1 engages the roller 22.1 by a predetermined amount beyond top dead center positively to lock the plate 14 in its operative position.