These pots were produced by Yixing Factory 1 during the 1977-1982 'Green Label' period. They were stored by a collector since then.
The teapots has red clay (Hong Ni) outside and purple caly (Zi Ni) inside, which called "Wai Hong Nei Zi" pot. It's a typical shuiping syle from factory 1 around that period.
The clay used by Factory 1 during this period was very good and these pots are nicely high fired which are well suited for brewing young and aged oolong, and all types of aged teas. Inside has a single hole filter, the wall is medium, the lid is loose as is usual for pots in this era.