Hi and Welcome!

As posted on U.S. N.R.C website:

"Commercial-grade dedication is a process by which a commercial-grade item (CGI) is designated for use as a basic component. This acceptance process is undertaken to provide reasonable assurance that a CGI to be used as a basic component will perform its intended safety function and, in this respect, is deemed equivalent to an item designed and manufactured under a 10 CFR Part 50, Appendix B, quality assurance program. This assurance is achieved by identifying the critical characteristics of the item and verifying their acceptability by inspections, tests, or analyses by the purchaser or third-party dedicating entity."

Mostly achieved by auditing process of supplying company.

Edit:More info about the overall process here:

http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-appb.html

Regards