LCA Bushings and Other Bushings

BergmanAutoCraft said

Keep in mind, the nut will tighten just fine with the suspension loaded and an air gun. For anyone considering this upgrade, delrin is a far superior material for this application. When using my pivots, the inner and outer shells are eliminated.
Lower Control Arm Pivots - Mopar - A Body - Bergman Auto Craft
BAC Delrin Lower Control Arm Bushings - Bergman Auto Craft

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So sell me on it. What's superior about delrin? Why aren't your pins greaseable? Does delrin not need grease? I get the strength thing. How so you eliminate the inner and outer shells? Through pin and bushing diameter? The bare bushing just presses into the control arm?