- Product Code: 55CA9CB
CMMG Nut, Receiver Extension, Mk4 - spare part for AR-15 platform, M4/AR castle nut for receiver extension (buffer tube), which locks the receiver extension and end plate in place. Part of the CMMG Mk4 system and generally compatible with AR-15 platforms; matte black finish provides a subdued appearance and surface protection.
This castle nut's steel construction withstands long-term use and repeated maintenance. The profile features notches for a castle nut wrench/armorer's wrench, ensuring secure and controlled tightening. Compatibility includes carbine-type receiver extensions (buffer tube), making spare part selection and installation easier.
Compatible with both mil-spec and commercial-type carbine receiver extensions, ensuring installation on most AR-15 lower receivers, including the CMMG Mk4. The castle nut works together with the end plate to prevent the receiver extension from rotating and loosening. The surface treatment is matte black, reducing reflections and being neutral with other parts. Not intended for rifle-length A2-type fixed stocks.
CMMG Nut, Receiver Extension, Mk4 - Features:
- Type: castle nut for receiver extension (buffer tube)
- Compatibility: AR-15/M4 carbine receiver extensions (mil-spec and commercial)
- Fit for manufacturer: CMMG Mk4 and other standard AR-15 lower platforms
- Material: steel
- Surface treatment: matte black
- Function: locks the receiver extension and end plate in place
- Installation tool: castle nut wrench/armorer's wrench
- Note: not suitable for rifle-length A2-type fixed stocks
- Manufacturer: CMMG
Summary: CMMG's castle nut is a reliable and compatible choice for AR-15 platforms when you want to ensure the receiver extension's secure locking and a neat matte black appearance. A solution suitable for both new builds and maintenance tasks.
Recommended use: recommended for AR-15 carbine-type receiver extension installations and maintenance, where the castle nut ensures the secure attachment of the end plate and buffer tube.
Product text updated 6.3.2026.
