An outdoor tool includes a powerhead, a tool unit powered by the powerhead, and a shaft assembly extending between the powerhead and the tool unit. The tool unit includes a transmission housing, a support plate, a guide bar adjustably supported by the support plate, a drive gear, and a chain circumscribing a portion of the drive gear and a portion of the guide bar, the drive gear operatively coupled to the powerhead. The tool unit further includes a tension adjustment mechanism for adjusting a position of the guide bar relative to the drive gear to increase and decrease a tension in the chain. The tension adjustment mechanism includes an adjustment screw, a threaded adjustment bolt, at least one adjustment gear, and a member coupled to the adjustment bolt and the guide bar. Rotation of the adjustment screw causes translation of the guide bar relative to the drive gear.