Billdit wrote:It was the "nest" I was referring to... You answered that question... Sorry I don't know the correct nomenclature ... I don't mean to confuse you JPG, another 50-60 years and I'll have this language thing down pat... I am going to pass on that 520 table conversion on Ebay... Will wait til I am more knowledgable ... Thanks for the help...
Truth be told, I made up the term 'nest' to hopefully help you(and me) understand what the 'rod slots' were. Billy is as guilty as I for making words up!
The boxy shaped rail extrusions have a curved surface along the interior top surface that the connecting tubes register against when the clamping screws are tightened from the bottom of the rail.
Way too much detail for either a salesman or their audience to comprehend, hence they use and make up buzz words.
The E-bay seller is being coy! The tables are of little use without an updated carriage.

Then again ignorance may be in the mix, but I doubt that considering his asking price for the carriage.

Keep looking, he was a bit too high anyway. If you get a sniff of another one, PM me and I will look at it. I do snipe on e-bay(last few seconds), but not for an item after another forum member has expressed an interest here.
BTW You did not confuse me,

Billy did!;)