Delrin is fairly slippery, my guess would be it's not surviving the rollers on the Post Office automated address sorting machines.
I've had no problem mailing P-shims, I use a bit of masking tape to secure them at the center of the envelope. I'll suggest that to Armory Craft.
When I mail members here a free 3.5mm ball bearing (used on the P938 trigger return spring as a follower to remove much of the "gritty"), I punch a hole in a bit of cardboard or foam, then put the ball bearing in that - - like that Delrin pin, it would never survive the P.O. experience without anti-angst padding!
BTW, the free ball bearing offer is still active, PM for address to send self-addressed stamped envelope if you would like one or two.
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