Redding Steel Neck Bushing Redding Neck Sizing Bushings are available in two styles. Both share the same external dimensions (1/2" O.D. x 3/8" long) and freely interchange in all Redding Bushing style Neck Sizing Dies. They are available in .001" size increments throughout the range of .185" thru .368", covering all calibers from .17 to .338 and clearly marked with size I.D. 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. Heat treated steel. The sizing diameters are hand-polished with a surface hardness of Rc 60-62 to reduce sizing effort .