Bore on the Tube? (7)
I believe the answer is:
calibre
'bore on the tube?' is the definition.
(I've seen this before)
'bore on' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for calibre that I've seen before include "Ability; barrel diameter" , "Personal character" , "Diameter of bullet or shell" , "Bullet size" , "Level of ability; bore" .)