Do you know what at 710 is?

From the humour file....

A few days ago I was having some work done at my local garage, when a young woman came in a bit flustered and asked for a replacement seven hundred and ten.
We all looked at each other and scratched our heads, one of the other customers asked her 'What is a seven hundred and ten?'

She replied, 'You know, the little piece in the top of the engine, I have lost it and need a new one..' She said that she did not know exactly what it was, but this piece had always been there but now it was gone and she needed a new one.
The mechanic gave her a piece of paper and a pen and asked her to draw what the piece looked like, she drew a circle and in the middle of it wrote 710.
He then took her over to another car which had its hood up and asked 'Is there a 710 on this car?' she pointed at the engine and said, 'Yes, its right there.'

If you don't know what a 710 is either: Click Here