This is the EQUATOR™ machine Fixturing plate (¼-20 in) #PCR-501212-50-20.

This fixture plate with kinematic location and imperial ¼ in. x 20mm threaded fixing holes. Using multiple plates per Equator system allows pre-loading of parts for shorter set-up times. This is particularly useful if quick-release fixtures are not used. In environments where widely varying temperature conditions necessitate frequent re-mastering, the master part can be permanently fixtured on one plate.