The Astro-Physics CNC machining center started with thick aluminum plate and carved out the excess material leaving a strong rib support structure. The finished plate is 0.75" thick, 14.75 " long and 6.5" at its widest point. The width of the plate tapers to 4.75". A pair of keyhole slots that measure 3.2" between centers are provided at each end. The distance between these pairs of holes is 13.75". Due to the ribbed structure, you may not be able to drill additional holes to suit your mounting rings. The plate weighs 2.3 lb. (1.0 kg.).
Since the rings will be spaced 13.75" apart (center to center), you can use the 15" Dovetail Plate (DOVE15, no longer available) as an accessory plate on top of your Astro-Physics mounting rings or Parallax Instruments rings with the Astro-Physics hole pattern.
Fasteners listed on Mounting Plate Fastener Chart