For iParts and Content Center we can use Custom Columns to allow users to type in a number instead of selecting from a pre-determined list such as Length, Width, etc.
We can only specify a range of numbers for that custom column and that range is used for every row of the table, there's no way to specify a range for each row. If I had a library of tubes and wanted to limit the 3/4" tube to a stock length of 10 feet and the 1" tube to a stock length of 12 feet it wouldn't be possible without having to split the libraries by size which is very inconvenient.
I think this can be fixed by allowing a Column name to be used as input for the range, this way the minimum and maximum of each range can be specified per row.