Elliptical expanders which are only used in bottle neck cartridges, will be the retainer for the decap pin in your Hornady dies. In most cases the expander is going to be .001” under the bullet caliber diameter. (For example a .224” diameter bullet would use a .223” expander.)

Note: This are for use in Hornady's Custom Die Series Dies, these will not work in the American Series Dies.