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 5915-00-644-0356
NSN 5920-00-849-7678
NSN 6240-01-499-1793
NSN 5910-01-433-8765
NSN 6220-00-272-7497
NSN 5855-01-398-9548
NSN 6650-01-533-7109
NSN 6110-01-583-5747
NSN 5990-01-414-7618
NSN 7035-00-529-3128
NSN 6110-00-816-9715
NSN 5998-01-055-6654