Examples of recoater carriages in an additive manufacturing system are described. In one case, a recoater carriage assembly has an elongate powder build material spreader, such as a roller, to spread powder build material in use. The recoater carriage assembly has a recoater carriage to support the spreader. The spreader is to engage and to disengage from the recoater carriage by movement of the spreader non-concentrically to a longitudinal axis of the spreader.