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 5835-01-614-1900
NSN 7035-00-104-7613
NSN 5999-01-380-9823
NSN 6130-01-388-6043
NSN 6320-00-593-0379
NSN 6610-00-739-1128
NSN 5975-01-335-2806
NSN 6645-00-163-4624
NSN 5960-01-436-0349
NSN 6320-01-215-1133
NSN 5990-00-155-2306
NSN 6320-00-937-5625