I have a used hitec servo MG but i dont know which one is the part number anywhere else other than the sticker? I just gigure its hitec because same color wires and fits same servo arms as my 645MG

Do you have a pic?

no not at the moment but it is the same case as my 645MG

Sometimes there's a printed number where the decal is. But a picture would be a big help.

If it is in the same case as your 645, then the servo can only be one of the following:
HS-625
HS-645
HS-5625 (digital)
HS-5645 (digital)