this is a especial insert nut for customers Straight wall, thru-threaded inserts designed in straight holes. Self-aligning lead-in provides for accurate alignment prior to installation. Thread sizes #0 to 3/4" and M1 to M16. left picture right is two poles of insert size we have ever produced the size of lesser brass inserts only is M1 and the big one is 3/4 inches we can provide more big size inserts as customers design