mounting a security door

ovahimba

I have been shopping around for a security grate for my back door. I am puzzled by the sizing of the frames. For a 36" door, the tubular frame of the security door has side mounting holes 37 1/2" apart. All the companies use these same dimensions. The problem I see is that 37 1/2" places the bolt right into the gap between the jam and jack stud where you have your shims. I thought these needed to be in the jack studs which would require a bolt spacing of 39". Am I missing something? Of course I can order a custom size which would cost an extra $800.