This is a 2"-24TPI male dust plug to protect diagonals/off-axis guiders/etc that would normally connect TO an SCT on the visual back threads. If the printed threads are not immaculate, it won't thread smoothly. I printed mine with PETG, but I am hesitant to recommend that. I think PLA or ABS might be better as those can be more readily "cut" by the receiving aluminum threads for a "tapped" result (just be sure to clean thoroughly afterward). Your optics handling are your own risks....