Sentence:  The tyres, which come from the steel manufacturers, are rolled without weld. They are bored inside to an internal diameter slightly less than the <WSD>outside</WSD> diameter of the wheel centre, on to which they have to be shrunk, the allowance being about <small>1/<sub>1000</sub></small> of the diameter of the wheel centre. 
Meaning of the word marked with <WSD> tags:  Of or pertaining to the outer surface, limit or boundary.