An AR-15 castle nut is a steel locking nut used to secure the buffer tube (receiver extension) to the lower receiver on AR-15 rifles. It threads onto the buffer tube, holding the end plate in place and ensuring a stable, secure connection for the stock assembly. The AR-15 castle nut works with AR-15 lower receivers, carbine-length buffer tubes, end plates, buffer assemblies, and collapsible stocks. It’s essential for building or maintaining reliable, adjustable AR-15 stock setups.
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