After looking at the first picture of the SX-28 on the Radio Boulevard that Jim Larsen just shared, it looks like Hallicrafters got the knobs from different vendors. Some were open and some were closed. They are solid on my SX-28. Dave N7RK -- Dave Hollander N7RK Arizona Tube Supply http://arizonatubesupply.com Ham Radio Page http://n7rk.com