ID was in the brass/copper area. When covered with dirt, looked like old shotgun shell cap. Surprised to see it isn’t. Very heavy for its size (about diameter of a nickel) due to thick walls. Small 5-point star in center. The inside has threads and the outside rim is knurled for gripping to twist. I’ve seen some very old electrical fuses that had screw-on end caps, but this just doesn’t seem like those. The top may have more small designs. I’ll try to clean better. Thanks
