Thanks Sweeney and Knotsaver. The round disc-shaped buttons closest to the centre are 9-strand under 3 wall knots which are then crowned. In the centre of each knot, to fill the gap, there is a small crown within another crown.
As to the grommet, I take it you mean the top central knot which is a covered ring within which is placed another disc-shaped button. The other knots in that top section are mostly cylindrical knots with a triangular cross-section. There are also small buttons which are made to fit neatly into the centre of these knots. Hope this helps.
Regards,
Joe.