Recoil Spring Plug from Sig 1911 We the people. Should also fit any 1911 pistol that uses this type magazine:

Fits many models including
Umarex 1911 M45 A1 CQBP
Umarex 1911 Commander
Milbro 1911
Swiss Arms 1911
Remington 1911
Sig Sauer 1911 with complete drop out (we the people)

Salvaged part.