The Nicest Savage No.4 Mk1* I've Ever Seen

[CINDERS]

It is the flat tie strap & rivet that goes across the back of the bottom wood where it meets the wrist which is what I think Ridolpho is referring to.
Also the chunky "S" in side the box under the wrist looks like it denotes a Savage Butt not a "Small" one if I am correct.