The flat-top SF130 range appeared in 1929. The yellow and black version is very rare indeed. As Mabie Todd did not assign different numbers to the different colours of hard rubber, I can only assume that this pen shares the /61 signifier with all the other HR pens.
Though they are not hallmarked the bands would appear to be solid gold. While there is a little wear there is no sign of base metal coming through.
Many thanks to Paul L for sight of this important pen and for his excellent photos.