Ha... err... the Norton 'Fastcut'. The original idea was to collect all of the regular range of Norton stones from the 1935 Catalogue
here. I was gonna leave out the 'Quickcut' because it's basically a Crystolon I think, but then noticed the FC was described in one part of the catalogue as a type of Hindostan. So obviously I needed that too!
The slight problem being I've never even seen a picture of one outside of this:
View attachment 179526
Pike FCs exist, and I'm going to be getting one soon from
@Skylar303, but that Norton version seems very hard to come by. I assume they discontinued it quite shortly after. But do give a shout if ever you come across one!