The L.E. Wilson Neck Sizing Bushing will allow the reloader to custom fit the L.E. Wilson Neck Sizer Die to any brass and bullet combination. To determine the correct size bushing, simply measure the outside diameter of the neck of a loaded round, then subtract .002" or .003" from the measurement. Since brass has a tendency to "spring-back" after sizing, this calculation will result in a consistent .001" to .002" inch of grip between the case neck and the bullet. Consistent neck tension is a key factor in quality bench rest loads.Notes: Freely interchange in all Wilson bushing type neck sizing dies.To Determine Bushing Size, measure the outside neck diameter of a loaded cartridge with a precision micrometer. From this measurement subtract .002" to .003", to allow for brass spring back and bullet tension.By selecting the correct bushing you can provide just the right amount of neck tension to properly hold the bullet without excessive resizing.