The number on your Smith & Wesson's yoke is called the "assembly number". ("Crane" is Colt nomenclature). If you remove your grips you will see that same number inscribed on the grip frame. It is also inscribed on the backside of the side plate.

The assembly number is used to keep these three matched fitted parts together during production. The number is not unique and can be recycled over months and years and used on another guns.

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~ S&W aficionado in training ~