4140 Alloy steel, black nitrided for wear resistance & corrosion resistance. Adds up to four more settings if your original only has two and has four more settings with reduced port sizes for customizing your settings to your ammo or suppressing.
 
Has the original two port sizes (regular and adverse) for a 550 or full length 556 rifle (as well as a few others in their list of models). This range of 6 settings should cover both long barrel and short barrel/pistol variants.
 
Ports are labeled by dot sizes on front of regulator using the spring detent as the “arrow” indicator for what setting you are on.

Port Sizes:
Port 1, 1.6mm
Port 2, 1.3mm
Port 3, 1.2mm
Port 4, 1.1mm
Port 5, 1.0 mm
Port 6, 0.9mm
 
Be aware: 
These regulators are the third run that have lockouts and require pressing the detent manually to move to takedown position. Also more aggressive lead-in chamfer for ease of install and optimized to get rid of tight fitment issues in certain rifles present in earlier runs.
 
These gas plugs do not fit SIG 553s.