Twin roll strip casting apparatus in which a pair of pool confining side plates (56) engage end surfaces of casting rolls (16) to form side confining closures for the pool. Plates (56) are mounted in side plate holders (82) connected to horizontally acting thrusters (83) which apply inward closure forces to the side plates (56). Thrusters (83) are mounted on a pair of carriages (101) disposed one at each end of the casting roll assembly and movable toward and away from one another to enable the spacing between them to be adjusted so that the carriages (101) can be preset before a casting operation to suit the width of the casting rolls (16). Carriages (101) are mounted on a central frame structure (103) which sits over the casting rolls (16).