NP127is bottom plate, also known as the Gib-5 Bottom Plate.
Diagram and usage notes
A - These accept the studs and guide pins on MRS-5000 mount rings for 5" tubes.
B - For use with the Tele Vue Gibraltar-5 Head. (Mounting instructions will come with the Gibraltar5)
C - For use with other Tele Vue Ring Mounts. (By using longer than normal studs, other Tele Vue scopes can conveniently be attached to the Gibraltar5 Head without removal of the Mounting Plate.)
D Tapped - For use with the Tele Vue’s Vixen Mount Adapter plate (AVT-1011) adapters for attachment to Vixen mounts.
E - For use with Vixen AM-AD-2576 accessory plate (discontinued).