I found and found it.
It is the only size suitable for desktop milling machine for this hobby
However, because the dimension D of the width of part A is about 1 mm higher than the milling table groove
It jumps out on the table (since it has only kore, it buys it with consent)
I am using that part with a grinder
I think that it was good that this T slot nut could be used as the standard accessory is just a square nut