A rotary cutting tool having a longitudinal axis and extending in a forward (D F) to rearward direction (D R), comprising: a tool holder, having a holder longitudinal axis and comprising a female coupling member having an internal thread extending rearwardly from a holder forward surface, the holder forward surface extending transversely with respect to the holder longitudinal axis; and a replaceable cutting head having a head longitudinal axis and comprising: a forward portion forming a cutting portion; and a rearward portion forming a mounting portion, the mounting portion comprising a male coupling member having an external thread and protruding rearwardly from a head base surface, the head base surface extending transversely with respect to the head longitudinal axis, and defining a boundary between the cutting portion and the mounting portion; wherein: the internal thread of the female coupling member is conical thread; and the rotary cutting tool is adjustable between: a released position in which the male coupling member is located outside of the female coupling member, and the internal and external threads (42, 72) are not threadingly engaged to one another, and a locked position in which the male coupling member is removably retained in the female coupling member with the internal and external threads (42, 72) threadingly engaged to one another; characterized in that the external thread of the male coupling member is a straight thread. a tool holder, having a holder longitudinal axis and comprising a female coupling member having an internal thread extending rearwardly from a holder forward surface, the holder forward surface extending transversely with respect to the holder longitudinal axis; and a replaceable cutting head having a head longitudinal axis and comprising: a forward portion forming a cutting portion; and a rearward portion forming a mounting portion, the mounting portion comprising a male coupling member having an external thread and protruding rearwardly from a head base surface, the head base surface extending transversely with respect to the head longitudinal axis, and defining a boundary between the cutting portion and the mounting portion; a forward portion forming a cutting portion; and a rearward portion forming a mounting portion, the mounting portion comprising a male coupling member having an external thread and protruding rearwardly from a head base surface, the head base surface extending transversely with respect to the head longitudinal axis, and defining a boundary between the cutting portion and the mounting portion; wherein: the internal thread of the female coupling member is conical thread; and the rotary cutting tool is adjustable between: a released position in which the male coupling member is located outside of the female coupling member, and the internal and external threads (42, 72) are not threadingly engaged to one another, and a locked position in which the male coupling member is removably retained in the female coupling member with the internal and external threads (42, 72) threadingly engaged to one another; characterized in that the external thread of the male coupling member is a straight thread. the internal thread of the female coupling member is conical thread; and the rotary cutting tool is adjustable between: a released position in which the male coupling member is located outside of the female coupling member, and the internal and external threads (42, 72) are not threadingly engaged to one another, and a locked position in which the male coupling member is removably retained in the female coupling member with the internal and external threads (42, 72) threadingly engaged to one another; a released position in which the male coupling member is located outside of the female coupling member, and the internal and external threads (42, 72) are not threadingly engaged to one another, and a locked position in which the male coupling member is removably retained in the female coupling member with the internal and external threads (42, 72) threadingly engaged to one another; characterized in that the external thread of the male coupling member is a straight thread.