Pot 1: 70's 80ml NWLJ Xishi - $200
Pot 2: 80's 70ml QSN Shui Ping - $180
Pot 3: 70's-80's 200ml Houhin Style pot for Japanese Export - $200
Buy all 3 and you'll get a solid deal.
Shipping from US, Buyer Pays shipping
Three Factory 1 Teapots
That was the official state factory producing yixing teapots between 1958-1998. In the 80's also Factory 2 and Factory 5 started their operation, and many other studios opened in the 90s. There were also some other factories producing plant pots etc., but in terms of teapots and quality F1 is the one.
Short story: https://en.wikipedia.org/wiki/Number_One_Yixing_Factory
It is the famous once state-owned factory where all Yixing were produced during a time, before the opening up and privatisation. Coveted, as the clay at the early period of the factory was/is supposedly different to modern Yixing.
More in-depth it becomes very fast a confusing and multifaceted discussion.