4mm. Handcrafted Solid 14k Yellow, Rose and White Gold with stainless steel threadless end compatible with 16g and 18g post/backing. 18k solid threads available for 18g, 16g and 14g threaded posts/backings upon request. Locally made in Downtown Los Angeles. Sold as single, threadless post/backing not included. (We do not make the posts/backings)