They have actually used three,
Uni loc, which they no longer use,
3/8X10 and 3/8X16 which when McDermott made McDermott, these two 3/8 inserts were the straightest well made inserts I have ever seen. You could spin the shaft between centers and the center matched the straightness of the thread. I sure do wish some one else who made quick release inserts would take a lesson from that.