Spikes Tactical Castle Nut - Lightweight - Phosphate. Spikes Tactical machined these AR15 Lower Parts from 4140 Chromoly material and then added a Melonite finish to resist corrosive elements. When you swap in this Spikes Tactical SLA501N Lightweight Castle Nut you'll reduce your build by 0.13oz in comparison to a standard castle nut. Save weight by using the sturdy and rugged Spikes Tactical Lightweight 4140 Chromoly Castle Nut. Specifications for Spikes Tactical Lightweight Chromoly Castle Nut: Manufacturer: Spikes Tactical Condition: New Country of Origin: USA Features of Spikes Tactical Lightweight Chromoly Castle Nut: Material: 4140 Chromoly Finish: Black Nitride Features: Machined Staking Notches Weight: .53oz Package Contents: Spikes Tactical Lightweight Chromoly Castle Nut Spikes Tactical SLA501N-LW: Castle Nut - Lightweight - Phosphate