Whilst it's strong enough to withstand the occasional car tyre, I have had to replace the plastic cover twice recently due to damage from a car tyre pressing a stone through it (I have a gravel driveway). As you can't buy the cover without a new frame, this is proving expensive.
I'd therefore like to upgrade to a ductile iron cover and have been looking at the Clark Drain CD 1649KMB (as it's a LOT cheaper than the Polypipe equivalent). I realise that I will have to change the frame too, but have a question about sizing. Clark Drain state that their frame fits a 300mm chamber. However, they also state that it is compatible with their PPIC bases and risers, all of which are quoted as 320mm diameter.
I'm wondering if the "300mm" quoted by Clark Drain is just a nominal size and whether their frame would be compatible with my 320mm inspection chamber? If anyone with experience of such things has any advice, I would be very grateful.