Hmm, ok. I'm afraid you'll have to excuse me for not having a Series parts catalogue to hand, and it also seems that I must apologise for not having clairvoyance enough to know either what your vehicle looks like or its' build history
Still, the part numbers are useful, so thanks for those. I still can't see how they qualify as standard, though. I can't recall seeing them fitted to other Series vehicles (obviously, or I wouldn't have had to ask) and they certainly weren't fitted as standard to any of the several Series vehicles that I've owned over the years. The only CSW I've seen them on were the ones I fitted myself, which hardly counts. On the listings I could find with a quick Google it seems that they were superceded by the other type quite some time ago. Perhaps you'd be kind enough to narrow it down a bit for me by saying what year and model yours' is.
On the plus side, I see Dunsfold list them so I know that they are still available, albeit at a price. Ho hum.