A spindle of a drilling tool includes a socket portion having a first axial length (a1) of a first diameter (d1) for receiving and attaching a drill bit to the spindle. The spindle includes a fluid conduit having a second diameter (d2) narrower than (d1) for conveying a fluid to the socket portion. An interface space with diameter (d1) is formed between the fluid conduit and the drill bit when the drill bit is installed in the socket portion. A fluid conveyor, having a third diameter (d3) narrower than (d1), connects the fluid conduit to the drill bit to avoid fluid gathering in a periphery of the interface space. The fluid conveyor includes a first O-ring abutting a mouth of the fluid conduit, a second O-ring abutting a mouth of a fluid channel of the drill bit, and a spring between the first and second O-rings.