Post #2 has correct stem, but is missing the bushing. Never buy RCBS parts from MidwayUSA. I usually get free parts from RCBS.

This is really simple. My 1980 RCBS 45 ACP carbide sizing die has a large entry radius. A knurled bushing with a 7/16" - 20 TPI outside diameter with a 1/4" - 28 TPI internal tapped hole fits in the top of the sizer die. The decapping stem is 1/4" - 28 TPI external threads with a large decapping pin. This decapping Assembly is a standard part from RCBS with bushing, stem, pin, pin retainer, and stem lock nut.

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S&WHF 366