Recently I've run across two variations of Redfield International front sights I've not seen before. Normally I've not seen anything on the left side of the base that attaches to the sight block. That is until today. I've seen one that is stamped 50 yd and another that is stamped 100 yd. My questions is, what is the difference between the one without a stamping and another that is stampted 50 or 100 yards?