This was the 'easy-set' toolholder, and designed to slap straight on to the topslide. Uses circular HSS. There's a photo of a set at the bottom of the page for this advert on 'lathes'…
http://www.lathes.co.uk/advertphoto/160415myfordaccessories/
Funnily, I have just acquired one of these to try. I have been using AR Warner HSS inserts to improve finish on an indexable tool, and thought I would give one of these older systems a bash.
Point is that it should provide for the simplest setting and regrinding of HSS tools for the less confident/ experienced, by which I mean me.
Cheers, Colin