Blue stabiliser
From Tardis Wiki, the free Doctor Who reference
The blue stabilizers stabilized the TARDIS and stopped it from shaking wildly whilst in flight. The Doctor stated that the blue stabilizers have no purpose, other being blue. River Song knew what they, supposedly before the Doctor, and used them to stabilize the TARDIS. After the TARDIS stopped shaking, the Doctor nicknamed them "blue boreingers", and said he found the journey no longer fun. (DW: The Time of Angels)
