Ed,
You said
I don't recall if the 505 had the holes in the table tubes.
I am not sure if you are referring to the holes in the Fence Rail Tubes for the Thumb Screw Locks for the Connector Tubes or the holes on the outer edge for mounting the Fence Rail Tubes to the Tables during the first year, but the Fence Rails were the same for both the 505 and 510. The 505 was kind of a step up from the original Table System AKA 500. Being cheaper it could attract customers not able to go for the 510. The 505 could later be "upgraded" to the 510 with the addition of the Floating Tables, etc. The 2006 505 I purchased several years ago was ready for those 510 additions.