The G20 magazine extensions that were being listed on myglockdoc.com are NOT compatible with G20 mags. I ordered two extensions from the site last week and they arrived today (shipped from Lone Wolf Dist.).
The packages are clearly marked for the G21, not the G20. I didn't open the packages and emailed the seller that replied that it was the right part, just that the packaging hadn't been updated yet. Well I opened one up and the springs are far too wide to fit into my G20 mags. Here are side by side pics with an OEM spring:
I emailed the seller and he claims that they should drop right in, and that he sells most of these to 10mm owners. Are any of them here? Cause I don't see any way to defeat the laws of physics and make these fit. BTW here is the a link to the Google cache of the sales listing which seems to have just disappeared their site:
The G20 mag fits into the extension tube, but I don't see any way that spring will work.