Oil filter problem

Post in tips and tricks on oil filters. Have a look HERE.

I have finally worked out where this mystery plastic bit goes. It is the guard that you referred to & is a perfect fit around the spring in the housing, however when this is fitted It is not possible to insert the filter as it is in the way.
I found this plastic guard loose behind the aluminium casing & I’m beginning to think that this was never fitted to the filter & was left there by a previous owner who had the same problem as me.
I have fitted the new filter without this bit & driving the car with no problems.
I would love to resolve this puzzle but I think this is going to remain a mystery.