Austro-Hungarian Mannlicher M1886 rifle iron sight.
<p>Left: main sight scaled at a normal distance (300 to 1500 steps)
</p>
Right: additional sight scaled at a long distance (1600 to 2300 steps)
<a href="//commons.wikimedia.org/wiki/User:Sumek101" title="User:Sumek101">Sumek101</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>