These are replacement twist knobs for Beckson portlights, but they could work on other manufacturer's portlights that use 1/4-20 threaded dogs.
Not just for portlights, they can also replace knobs on roof racks for skis, Bimini tops, barbeques, and more — anywhere a 1/4-20 threaded stud is used.
• Twist knobs have a stainless steel insert nut; twist knobs assemblies add a 1/4-20 SS toggle bolt and a portlight frame pin
• Both twist knobs and twist knobs with hardware are sold in pairs
TIP — When replacing these knobs, you will need to know that the terminal threads on the stainless steel 1/4-20 threaded toggle are crimped to prevent the knob from accidentally being lost.
To remove the knob, you will need to reshape the crimped threads with a die, or triangular file.
Alternatively (but not as good), you can carefully unscrew the knob until very firm resistance is encountered, reverse direction until the knob spins freely, unscrew the knob again until firm resistance is met, reverse again. Keep repeating this until you have forced the knob past the crimped threads.
Work gloves will help.
More complete instructions are available from Beckson.