<p>Hands-on interactions provide a fundamental bridge between action and cognition, offering sensorimotor information that shapes how humans perceive and mentally represent their world. To directly probe this relationship, we used a naturalistic task in which patterns of hand use were measured as participants (<i>N</i> = 65; 37 females) reached for and grasped toy bricks to construct replicas of a model that varied in spatial complexity, requiring either low or high levels of mental rotation (MR). Participants also completed the gold-standard test of MR ability (MRT). Because spatial abilities such as MR are predominantly right-hemisphere lateralized, we predicted increased left-hand use (controlled by the right hemisphere) when grasping toy bricks in models with high MR demands. The results confirmed this prediction, but only in males; males increased left-hand use under higher MR demands. Exploratory analyses further revealed that, specifically in younger males, this behavioural shift predicted MRT performance, indicating stronger right-hemisphere specialization and tighter action–cognition integration. Together, these findings demonstrate that a fundamental sensorimotor behaviour such as grasping provides a window into spatial–cognitive processing, with patterns of hand use reflecting hemispheric specialization and predicting individual differences in MR ability, providing direct evidence thereof.</p>