At the time I announced an #InstallationFAIL upon the Sig Slim-Grips I had purchased I received some feed-flack from a know-nothing fanboy who derided my choice of purchase venue: eBay.
But they were the Full-Factory Original Thangs – just not at factory price$ that I can’t afford.
The mounting problem stemmed from an unannounced (to me anyhow) Sig modernization and manufacturing change, from the old steel mainspring-strut to something rather different.
Anyhow the old grips fit but new ones didn’t and here’s a closer examination and visual explanation of how and why it worked (or didn’t).
The rear profile of the old grip is noticeably fuller to accommodate the old-style strut, and the new “Slim” grip is unable to maintain that voluptuous contour.
Not Clauswitz 
Hey Anon, thanks for that tip! The reduction in grip circumference is good and aids to “grippabilty” – or whatever you want to call it..
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You can swap old for new and back again if you wish. I've changed out a couple of my older style mainspring assemblies for the newer kind to get around the grip problem.
I also think the newer style gives a better trigger pull, but that's probably just me.
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