Ian G

During my last service, the garage found that the power steering belt tensioner had siezed and snapped off. This was a small plastic bit with a long bolt through. They have now sent me a replacement, which is a metal cubed shaped bit roughly an inch square.
Is this correct?
I was told this is a common fault, so is this new metal bit a design improvement - or is it the wrong bit?
Any help today please, otherwise I'll get back to the garage tommorow.
Cheers,
Ian.