Stud backings
Push backs are the most common and the cheapest; screw backs hold more securely for higher-value studs; butterfly backs are easy for the wearer to handle. Post length and thickness affect comfort as much as the backing type.
For pierced ears the post is the part with the tightest nickel restriction, so specify post material explicitly.
Hoops and drop styles
Hoops rely on hinge and click closures, which need a positive click and consistent tension. Drop styles hang from a wire or a small loop, and weight is the main comfort factor.
Test closures on the sample: a hoop that opens too easily becomes a return, and one that is too stiff discourages the wearer.
Cost and packing
Backing choice changes cost per pair more than most buyers expect, because findings are bought per piece. Pairs are normally packed on a card, which also carries the material and origin information.
Agree the card, the pair orientation and the backing type in the packaging proof so the packing line does not improvise.