This is a high quality, aluminum muzzle brake compensator.  It is made in the USA (Minnesota actually).

Features include:
 
  • 9mm or .380 caliber
  • threaded for 1/2"-28 tpi right handed threads (most common 9mm threads in US)
  • COUNTERBORED: this feature on the slide facing side lets the brake get closer to the slide to make the gap smaller!
  • width is sized to match the Glock 43, but looks and works on other glocks and other 9mm pistols (0.85" wide)
  • flush with the top of the glock slide
  • distance (or gap) from the front of the slide depends on your particular barrel but is reduced by up to 3/16" because of the Counterbore.
  • add just 0.85" to the length of the threaded barrel
  • Made of 6061 Aluminum
  • Anodized black hard coat type III
  • held on with #10-32 x 3/16" nylon tipped set screws (so it will not scratch barrel threads) (included)
    tighten set screws to 10-12 inch pounds

This reduces felt recoil for competition, or duty.  Works better with higher grain/higher power loads (they have more gas to push back against the brake with).  In some cases, very light gamer loads will not cycle the action unless springs are changed out.

Set screws are tightened with a 3/32" allen wrench (included).  When tightened down the tops of the allen screws are below flush with the side of the compensator.  On screws this small about 10 inch pounds is all the tighter you want to get them.
You can loctite the set screws and the comp on if you want with temporary loctite (included).