UnknownVT, ok here goes.....
**this will work on 600 series and i would think 400 also**
1- remove the plier jaws. (by unsnaping the black clips on either side, much like a master-link on a chain)
*!*!* be sure not to loose the little springs under the "release studs"*!*!*
2-with the jaws removed, take a pair of "channel locks" or similar plier and GENTLY squease the handle pivots. do this until the jaws will just slide in and out of the handle.*this takes care of the side-to-side play in the jaw section.
3- reassemble the plier jaws. *note: the black clips go on as to have the open ends facing (pointing) to the jaws.
*now for the up and down play (i use this term because i'm an idiot and don't know the correct term)
4-after reassembly, you will need two (2) 3/16 cir-clips / c-clips. just slide these under the leading (open) end of the black clips.
**this should tighten up everything and still slide/one-hand open.
**may take some break-in
Whew!
![Eek! :eek: :eek:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)