Pin tumbler lock system and a key pin for such system

A pin tumbler lock system for a lock, said system comprising

• a housing having at least one first housing channel and at least one second housing channel, the housing having an inner surface and an outer surface, the second housing channel extending from an aperture in the inner surface to an aperture in the outer surface;
• a plug rotatably mounted in the housing, said plug having at least one opening for a key and having at least one first plug channel that aligns with the first housing channel along a shear line between the plug and the housing, the plug further having at least one second plug channel;
• a tumbler pin set comprising a driver pin, a key pin, and a spring member arranged in the first housing channel for extension into the first plug channel, such that the plug is in a locked position, wherein rotation of the plug is disallowed, when the driver pin extends into the first plug channel, and the plug is in a unlocked position, wherein rotation of the plug is allowed, when the gap between the key pin and the driver pin is aligned with the shear line, which can be realized by insertion of a proper key;
• wherein said key pin comprises
• a first key pin member with at least one internally threaded portion,
• a second key pin member with an externally threaded portion for engagement with the first key pin member, and
• a rotation prevention means for preventing the key pin from rotating when mounted in the housing channel and/or plug channel, said rotation prevention means comprising a side protrusion protruding from the key pin and a side groove arranged in the housing channel and/or plug channel for receiving the side protrusion of the key pin;
• and
• the second plug channel being aligned with the second housing channel such that a one of the key pin members is engagable by a tool through the aperture on the outer surface of the housing.