Timing belt idler pulley KV6 2.5

[barry]

Greetings.
I have been gathering a few bits over time with the view to eventually replacing the engine timing belt.
Have just purchased the timing belt idler bearing.
The diameter of the new item appears to be a couple of centimetres less than the item it is replacing. The image (pt.no. LHV100110) on the Rimmers website appears very similar to the idler I have just purchased but this could be deceiving.
Were there two different sizes used on the KV6 or do I return the new item?
This assumes also that I am looking at the correct pulley down in the maze.
Thanks for any input.

Barry