Shell component of a type 1 encapsulin nanocompartment. Assembles into proteinaceous shells 23-24 nm in diameter with 2-2.5 nm thick walls. Cargo protein Flp (ferritin-like protein, may store iron) is targeted to the interior via its C-terminal extension. This encapsulin nanocompartment is formed by 60 subunits; monomers form pentamers which assemble to form shells. There are 12 pores where the pentamers meet as well as 3-fold axis channels and dimer channels; none are larger than 3-4 Angstroms in diameter. The N-terminus of the protein is inside the shell, the C-terminus is outside. Belongs to the encapsulin family. Family 1 subfamily.