The two raised surface features are .250-20unc-2b
A metallic or nonmetallic item which is rigid, flat and generally smooth. Its thickness is small in comparison to its length and width. It is designed for mounting another item and may have drilled or threaded holes or other facilities for mounting to a supporting object or surface. See support, as modified. Do not use if a more specific name applies.
NSN 5855-01-459-9254
NSN 5950-01-193-3276
NSN 5905-00-849-3229
NSN 6645-01-298-4662
NSN 5996-00-278-5193
NSN 6130-01-360-7218
NSN 5920-01-336-1730
NSN 2925-00-127-7828
NSN 5985-01-341-7387
NSN 6320-01-459-6992
NSN 6610-01-390-6925
NSN 5999-00-052-0915