The Fortis Manufacturing Standard Castle Nut secures the receiver extension (buffer tube) to the lower receiver on AR-15 and AR-10 platform rifles.
- Part Type: Castle Nut
- Compatible Firearms: AR-15, AR-10, and other AR-pattern rifles
- Material: Steel
- Finish: Manganese Phosphate
- Installation: Requires AR-15 armorer’s wrench and torque wrench; staking recommended
- Includes: (1) Castle Nut
