Character is bore on the tube (7)
I believe the answer is:
calibre
This might be a double definition.
'character' is the first definition.
(I've seen this before)
'bore on the tube' is the second definition.
'calibre' can be an answer for 'bore' (gun terminology). I'm unsure of the 'on the tube' bit.
'is' is the link.
Can you help me to learn more?
(Other definitions for calibre that I've seen before include "bore on the Tube?" , "Diameter of a gun barrel" , "Quality of character" , "Level of ability; bore" , "Bullet size" .)