Yes, the 5/8" adaptor stud is detachable. It is similar to a Matthews or Avenger stud. The base can be used with longer columns. I have not tried Matthews or Avenger columns, but I have used the JTL stud in Matthews stand on occasions. I would think that any equipment conforming to those standards would inter-fit.
Thank you for your very prompt and useful answer.
I live in Europe, I have to deal with "European" prices so sometimes I buy items from abroad to cut expenses and I wish to be aware of what I am going to buy.
Now, concerning C stands "standardization" one might encounter ugly surprises, for instance Chinese Fancier C stands,#FS9101A,(I presume copies of Chinese Kupo's) have slightly larger receptacles for columns than 1-1/8".
So I think one cannot mount their columns on Avenger, Matthiews turtle bases.