For use with RCBS Gold Medal Match series dies. Works in both the full length and neck sizing styles. To find the proper neck bushing size, measure the outside neck diameter of a loaded cartridge and subtract .002" to .003" to allow for brass spring back. RCBS suggests having have neck bushings one or two sizes above and below your target diameter to ensure the perfect fit.Neck Bushing Size (RCBS instructions):Proper neck bushing size can be determined two ways. Measure the outside neck diameter of your loaded cartridge, subtract .002" to .003". This allows approximately .001" of brass spring back for correct neck tension. The other is to measure the neck wall thickness of your case, multiply by two, add the diameter of your bullet and subtract .001". RCBS suggests that you have neck bushings one to two sizes above and below your target diameter. Notes:Tungsten Disulfide has an extremely low coefficient of friction (0.03, titanium nitride is 0.6). For u...