Redding Neck Sizing Bushings are freely interchange in all Redding Bushing type Neck Sizing Dies. By selecting the correct bushing, you are now able to provide just the right amount of neck tension to properly hold the bullet without excessive resizing. Made of heat treated steel. The sizing diameters are hand-polished with a surface hardness of Rc 60-62 to reduce sizing effort. The proper bushing size can be easily determined by measuring the outside neck diameter of your loaded cartridges with a precision micrometer. Then, simply subtract .001" from the cartridge that had the smallest average neck diameter. Moly coated bullets may require tighter necks and the use of bushings .001” or .002” smaller.