Both Southards I've owned moved side to side when closed, minimal but definitely noticeable. When open, no blade play at all of course, very solid.
F&F is good, but not as good as some people make it out to be.
Here are some noticed issues:
1. Milling can be seen in the thumb cut out.
2. Milling can be seen in the titanium liner sides.
3. Finishing inside is good but not great. Could have seriously used chamfering.
4. Better fitting of the lanyard tube.
5. Fit on the knife is very good but not great, yes it's tight but it isn't because tolerances are tight, it's due to the pressure in the lockbar holding the knife in place not tolerances.
6. Fitting of the pivot is poor imho, plenty of play of the two I owned. Made playing with the pivot to center the blade a bit toy like.
7. Pocket clip is sharp and will poke through denim jeans.
If you take a Southard, properly disassemble and reassembly or tighten or loosen the pivot it properly you can affect the blade play, and centering easily enough.
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I think you are being very picky about the Southard!
I have a little side to side play in mine too. I didn't even check it until I read about sts play in your post.
The list goes on about being overly critical of an excellent knife IMO.
I could say a Lot more about some critical comments in your post.
I don't think most members checked out their Southard's as tho they were trying to find 'tiny defects'....and then post them on this thread.
One of our most famous president's said " you can't please all the people, all the time."................................