This Sig 556 stock block is used to prevent the folding of the stock on the Sig 556 rifle. This is necessary in cases where the overall length of the rifle would otherwise be less than the California minimum of 30" when folded. The block is installed inside of the spring behind the stock release button and prevents the button from being depressed.
1) Use a punch to drift out the stock hinge pin and remove the folding stock assembly.
2) Remove the stock release button and spring
3) Put the stock block inside of the spring and reinstall the release button
4) Slide the stock assembly back into place
5) Use a punch to reinstall the stock hinge pin