I was sorting and storing my test leads tonight after the big DMM consistency check, and realized I had a pair (probably came as part of a bundle with my Fluke 179 pawn shop purchase) which I hadn't tested yet. They have no branding whatsoever, just the part number TL-99-1. I plugged them into one of my meters and - the plugs didn't seat fully. In fact, they wouldn't go into any of the guarded receptacles far enough to make electrical contact! I pushed pretty hard (on one of the cheaper meters, not wanting to damage an expensive one) and still nothing.
Here's a picture of the plug (left) next to a Fluke plug. It sure looks like the contact pin is too large but the guard is comparably sized. Also attached is a picture of the probe end - looks properly marked but could be a fake I suppose.
Is there a different sized test probe pin that I'm not aware of? I have no idea where these came from originally. All my other guarded probes, including some pretty cheap ones, have no trouble fitting any of my meters.