BS 3A 210:2019 Aerospace series. Nuts, hexagonal, ordinary and thin, Unified threads (below .250 inch) in brass, tin plated. Specification

Size
Brass
Threaded fasteners
Fasteners
Threaded components
Aircraft components
Designations
Protective coatings
Dimensions
Hexagonal-head fasteners
Internal-thread fasteners
Nuts
Unified screw threads
Air transport engineering

Link: BS 3A 210:2019 Aerospace series. Nuts, hexagonal, ordinary and thin, Unified threads (below .250 inch) in brass, tin plated. Specification
Source: BSI Standards