The plug going into the bottom of the stock at right angles to the lower recoil pad screw is filling the hole where the original Fraser sling eye was placed. They are a normal eye, but set almost flush with the toe line of the stock.

If you want to tighten the through bolt, the pad will have to come off so the bolt can be taken out. A different thickness washer will have to be used under the head so the hole for the hand pin will line up. If the stock or bolt is even the slightest bit loose, it needs to be done.

You may as well do the triggers then.