have had numerous folding draw knives i have either traded or given away. i did keep one and use it periodically. the bolts are square as is the "hole" in the handles. once the wing nuts are tightened down the handles have no movement at all. makes a bit easier to toss in the tool bag. some of the other ones didnt hold as well. some did. some had serrations to hold em open or closed, those had the most "play"
yeah finding em cheap is hit or miss these days but as mentioned on previous threads, there are many on that big auction site and seem most i have watched go for under $20. in this part of the country it is still relatively easy to stumble on em at flea markets and swaps etc for less than $10. antique stores seem to be a bit more in the $20 range. tho ive seen em for up to $50. they were such a common farm tool back in the day, there are lots of em out there. unless they have bad nicks or have been sharpened to nothing, they work just like when new. and better than modern imho. but i do like old tools, so have no need to pursue newer tools.