This Lilja thread protector is 1/2 x 28.The thread protector is built to match AR barrels in front the gas block section and 1/2" - 28 TPI threads. Machine using the same steel as Lilja's rifle barrels, the thread protector is milled with an 8" twist rate, just like the rifling in Lilja's .223, 6.5 Grendel, and .260 Remington AR drop-in barrels. Dimensions: 1 x 1 x in, Weight: 1 lbs. Lilja Thread Protector 1/2 x 28