Ok here is another issue.
I have taken the liberty to do some good compares and the results speak for themselves. As previous mentioned items like 'cost' can also be explained in the below photo's.
Here we have TBC and mandrel bushings for the Gent Jr/Statesman Jr/Venus and related pens.
This is for the 7mm slimline, euro and related. I included a single 7mm slimline bushing and not the entire euro bushing set. The object in the bottom center is a euro mandrel, it is used to turn the end cap on a euro with a post stud. The TBC bushing set is the
'7mm triple play' set by JohnnyCNC. The rings in the center are sizing washers also from JohnnyCNC.
As you can see the advantages of TBC is LENGTH inside the tube yields a longer, more stable and more accurate precision. Also the section outside is greater as well, this yields not only space between the dead/live center and provides extra tool rest support but also comes in very handy when hand sanding.
I have noted several times with a mandrel setup there is some wobble of the bushings because of the short length. If the mandrel shaft is not proper size there will be warping of the blanks.
Ed