The RetroArms body pins lock themselves, so when you tighten the pin into place with a screw, it attaches firmly to the receiver and removes wobbling between the upper and lower receiver!
The pins themselves are made of aluminum and the pin screws are made of steel.
RetroArms – CNC Engineering at Best
RetroArms is a Czech airsoft company which manufactures high-quality upgrade and spare parts. The company has become known from its CNC machined parts, especially its super durable gearboxes which are made from 7075 aluminum. RetroArms gives its gearboxes a lifelong guarantee against breaking which tells us a lot about the quality of the parts!