Hi Christine,
Thanks for taking the time to leave a review! These flat back posts are 18g thick, and are compatible with 18g push-pin style flat back studs. Because of differences in gauge and mechanics, these backs aren't compatible with threaded earrings, or butterfly back earrings. Let us know if you have any additional questions or concerns. We'd love to help! <3
Best wishes,
Elizabeth with Cords Club
“I have super sensitive ears and I haven't worn earrings in years because Ive reacted to everything I've tried. But I don't react to these at all!! I'm so happy to have found earrings I can wear!!”