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 type Neck Sizing Dies.They are available in .001" size increments throughout the range of .185" thru .365", covering all calibers from .17 to .338.
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.
TO DETERMINE BUSHING SIZE
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.

Bushing Reference Chart