5/16 inch inside of snap for all three sizes. Choose length. Die Cast from a Zinc Alloy and then nickel plated to a high luster on the standard snaps / the brass version is solid brass. Henssgen Hardware's Zinc Alloy is rust proof and is used outdoors in fresh water and salt water environments. To add to the rust proof quality Henssgen Hardware equips each Die Cast Zinc Alloy Snap with a Stainless Steel Spring. Double End Brass Snaps are used to hang feed buckets for Horses and as gate hooks. Sold as eaches