[r-t] pure triples

[Alexander Holroyd]

What is the simplest extent of pure triples?

Obviously the meaning of "simplest" is subjective, but what I am driving 
at is that the construction should be straightforward, and should not 
require an extensive computer or hand search, and it should be 
self-evident that it works.

Also, how many fundamentally different extents of pure triples are 
popularly known?  Not many it would seem...

Ander