Corsa-B.uk - Vauxhall, Opel and Holden Corsa B Owners Club

Just had my alternator tensioner replaced due to the bearing going and it making a screeching sound. All seems a lot better. However when the mechanic had fitted it, he removed this pin from the top of the spring. Its was about 3cm long and not really very thick. He said it makes the spring extend and gives the tension. Is this correct? As the way i thought it worked, the metal rod going through the middle of the spring hooked over the pin therefore removing the pin would make it all come apart.

Found a picture on the internet but can't see where the pin is.

Blue - Where i thought the pin was.
Orange - Metal Rod

http://tinyurl.com/yeyk7n4

Its driving me and my dad crazy.
Many Thanks.