These sling swivels will work on a Brown Bess Musket.You may have to drill the hole a little larger on some muskets to get the screw to fit through the trigger guard or stock. They are made of steel with threaded screws which measure at 0.186. The diameter of the swivel is 0.178.The forearm swivel is 1 1/8" wide on the inside of the swivel with the height being 1 1/2" , trigger guard swivel measures 3/4" wide on the inside of the swivel and 1" in height.The swivels will accept a 1 1/2'' leather sling. We make our slings 1 1/4' wide and they work well with these swivels.