I had this plate custom made because I wanted my rings placed further apart on the OTA than the standard Giro mounting plate would allow. The total length of the plate is 9 1/2". The sets of holes for mounting the rings are 8 1/2" apart center to center. The hole pattern is for TMB rings which I'm told are the same as AP and Takahashi although I don't know this for sure. See measurements below. The plate is made from solid aluminum and is 3/4" thick. It bolts directly to the Giro arm. I paid $75 to have this made and will sell it for $50 + shipping.
Outside holes for mounting rings are 2 3/8" apart center to center
Outside hole is 1 3/16" center to center from the center hole
Holes for mounting to Giro arm are 1 7/16" apart center to center
All holes are 1/4" diameter