Heavy Duty Insert. **Acme product is dual certified to specific mil-spec certifications. For questions regarding certifications, please contact our customer service team at 800-323-1232. Acme’s MS/NAS Style Inserts are produced to the following standards: MS51830, MS51831, MS51832, NAS1394, NAS1395, NA0146, NA0147, NA0148, NA0149, NA0150, and NA0151. Acme also has Keylocking Studs produced to the following standards: MS51833 and MS51834.**