I'm not sure what to call this, but it's the hawse pipe cover, aluminium suitable for a hawse pipe hole of 65 mm. It looks like this, but has SL (Simpson Lawrence) stamped on it:
http://www.marinemegastore.com/produ...jump=0&cat_id=
It's brand new, bought some years ago but not used. Part of an ongoing garage clearout. £20 posted UK
Chain pipe cover
Threaded Mode