Disclaimer: Standards are subject to revision. Always check with the ECIA for the most current version of the standard.
Measuring 0.375" x 0.375" (9.5 mm). These are standard in modern data centers and utilize snap-in cage nuts. Eia Eca-310-e Pdf
Enterprise RFPs (Requests for Proposal) frequently require vendors to certify that their enclosures or hardware comply fully with the ECA-310-E specification. Disclaimer: Standards are subject to revision