A tool holder assembly includes a holder body, a pull stud and a flow adjustment unit. The holder body has a holder coolant channel extending through a first end and a second end thereof. The pull stud has an insertion portion, a grip portion, and a longitudinal passage extending through the insertion portion and the grip portion, and fluidly communicating with the holder coolant channel. The flow adjustment unit includes a connection tube that extends into the longitudinal passage and projects outwardly from the grip portion, a resilient member urging the connection tube to project outwardly from the grip portion, and a flow guide channel extending through the connection tube and fluidly communicating with the holder coolant channel.