I figured that I might as well make this public knowledge. 5 of them are 1/2x28 and are big enough for .30cal although they all came off of 5.56. I have one that is 1/2x28 and it is a true .223cal size hole. I have one that is 5/8x24 for .30cal and finally one is for an AK threaded M14-1LH.