No one said what they do - but that's ok. I've used stain to try and hide it. I once looked at a gun that Brad Bachelder had put wood on the space right behind the receiver on each side on a box lock to hide the bolt going through. He did such a good job I couldn't see the glue line. I was amazed. I believe he once said he worked for "Grand Rapids Furniture " and that would explain a lot. Paul