From Ammoland:

The guide comes from the NYPD Intelligence Division and aims to help officers identify PMFs. Although the intention is to help police identify PMFs, it reads like a “how-to guide” to firearms building. It lists all the parts needed, where to get them, and examples of homemade guns.

The guidebook calls out several manufacturers, including Polymer80, Glock Store, Strike Industries, 80 Percent Arms, Lone Wolf, Geisler, and JSD Supply. The guide includes a handy list of the companies’ websites and their products.