The online community of knife collectors, A Knife Family Forged in Steel
Until recently I had never heard the term "slip joint knife". At first I thought it must be a type of knife that opened differently than a standard pocket knife. From my own research I think I have learned that it is just another term for a non locking folding knife. Is that correct or is there some difference between the two?
Yep. Non-locking folding knife. It's an old timey term.
Another one to consider is "Jack" knife--not all slip joint folders are Jackknives!
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