These K Model tappet covers need to slide together easily (no binding) to function properly. They must be almost perfect. These were "far from perfect." The smallest dent can render them sticky, almost useless. The threads must be perfect too. The smooth, inside covers are installed under the valve guide flanges, with a fiber gasket between the cover and the cylinder. I've got a few hours in these. They are nice. Painted with a light coating of Hi-Heat H-D Barrel Paint Silver. I prefer the original H-D parts. It's worth it to repair them. Aftermarket covers would probably need to be worked to fit anyway . . . so just use the real deal.