Help Needed!!! For This Particular IWC Strap

Dear All,

Please help to identify this particular IWC leather strap for which model? and why have extra steel part attached to leather strap. Thank you in advance.
Leather width size is 19mm
Tang buckle is 16mm

Welcome to the forum. The strap is a regular leather 19/16mm strap, The finials are to install the strap into the SL Ingenieur, e.g. Ref 3506, 3508 etc, that also come with a steel bracelet.