I assume fietsbob meant the Brompton saddle pin adaptor



It has been discontinued a while ago.

From an old Brompton manual:

"Saddle adaptor pin (125 gms)
a) mounted "pointing down", it allows the saddle to be moved up
to 40mm forward (which also makes the folded package the
most compact)
b) mounted "pointing up", it allows the saddle to be moved up to
30mm higher, albeit slightly further forward."