Barrel Question

[Yugo]

I have a SOTA ARMS upper with a 1to9 twist and I want to replace the lowpro gas block with an a2 style sight but I dont have a caliper to measure the size and dont know which to get.

http://www.midwayusa.com/product/628449/doublestar-a2-front-sight-gas-block-with-bayonet-lug-ar-15-lr-308-750-inside-diameter-steel-matte

or

http://www.midwayusa.com/product/410205/doublestar-a2-front-sight-gas-block-with-bayonet-lug-ar-15-lr-308-625-inside-diameter-steel-matte

or you tell me???? please help thanks in advance.

[6mmintl]

Try a micrometer to measure barrel, beg/borrow one.

[kcstott]

With a 1/8" difference you should be able to eyeball it with a tape measure. Or put a wrench on it. You just need to know if it's 5/8" or 3/4" just use a wrench