These are the Guardian II Positive locking 6.1mm outside diameter earring backs with Comfort triggers that fit a 0.89mm diameter post. They are also
14KY,14KW,18KY & 18KW Guardian II Positive Locking 6.1mm Earring Backs
Hold Me Tight Earring Backs – Oradina
Flat Back Studs – Grayling
200 Pairs (400 Pieces) Stainless Steel Earrings Posts
102pcs Comfortable Impenetrable Soft TPE medical grade material (same as pacifier material) Earring Backs (Better than silicone material) Sleeping
102pcs Comfort Impenetrable Soft Safety Backs TPE Medical Grade Material (Same as Pacifier's) Fit with All Types of Earrings
Angel 18K Gold Screw Back Earrings
Gold Stainless Steel Bullet with Plastic Disc Earring Back - 100 piece – Clay Craze Studio
Tips and Tricks to Wearing Flat Back Earrings
Nap Earrings
Flat-back Earrings in Assorted Designs