Two-for-one twisting spindle having a pneumatically actuated threading device, with a spindle shaft rotatable about a vertical axis partially configured as a hollow shaft with a lower feed bore extending coaxially to the rotational axis, and with an injector element opening into a thread guide channel of a thread guide ring temporarily connectable during threading to a compressed air source. Part of the compressed air feed to the injector element is formed by the feed bore. The compressed air feed comprises a connection element (27) with a curved air channel (26), which connects the feed bore (24) to the injector element (16). The connection element (27) is configured as a separate component and the air channel (26) is adapted to the flow requirements.