Micro low-profile .750" gas block for AR-15 barrels with a .750" journal diameter. The compact profile sits well under any free-float handguard, which is exactly what you want for a modern build using an M-Lok or KeyMod rail instead of a triangular FSB.
Slide onto the barrel journal, align with the gas port, and pin the gas tube through the block. A dimpled or pinned barrel gives the most secure hold and rules out gas block shift under sustained fire. Use blue thread-locker on the set screws if your block ships with them.