BS EN 4123:2018 Aerospace series. Shank nuts, self-locking, in heat resisting nickel base alloy NI-PH2601 (Inconel 718), silver plated on thread. Classification: 1 550 MPa (at ambient temperature) / 600 $0DC

Fasteners
Dimensions
Silver
Metal coatings
Heat-resistant materials
Surface treatment
Aircraft components
Nuts
Threaded fasteners
Nickel alloys
Coatings
Marking
Designations
Locknuts

Link: BS EN 4123:2018 Aerospace series. Shank nuts, self-locking, in heat resisting nickel base alloy NI-PH2601 (Inconel 718), silver plated on thread. Classification: 1 550 MPa (at ambient temperature) / 600 {$permalink}DC
Source: BSI Standards