It's a cut down Long Lee Enfield /Lee Metford rear sight base - still showing 200yds (the full length sight base will go up in 100 yd increments to 500yds or 600yds). The flip parts are not military. The screws on the sight bases are at the rear(possibly still present to the right of your picture) and the front (now missing). If it isn't obvious it's been cut off. Heat it up, melt the solder and you're good to go.
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