Mules are needlessly confusing. Please explain. PMG article is not enough.

[Luckyjeff]

From what I have read concerning Mules, about every article differentiates between the size of the micro numbering between the front and the back of the note and whether it is .6mm or 1mm and also indicating that the microprinting was switched to the larger size 1mm.  My problem is that there are TWO plate sets on the front and one on the back.  On my 20's, the left side of the front has the number next to "E" as a .6mm and on the right side, the number next to the letter is 1mm.  How do I compare the back with the front when the plate on the front has a micro number on the left side that is smaller than the micro number on the right side???

Also, I got the impression that .6mm micro plate numbers were phased out in the newer bills which is fine but my 2013 One dollar bills have .6mm Plate stamp numbers on the right side of the bill.  That is two different sets of 2013 with two different Federal Reserve branches:  San Francisco and Philadelphia.  The left side plate stamp on the one's are the larger 1mm that matches the 1mm on the back.  In summary, I have $1, 2013 bills with .6mm on the right front, 1mm on the left front and 1mm on the rear AND $20 bills from 2017 with .6mm on the left front, 1mm on the right front, and 1mm on the rear.  ALSO, I have 2013, $20 bills with .6mm on the left front, .6mm on the right front and .6mm on the back.  WHAT'S UP???

Thank you for any feedback 

[asdfgh]

For $1 bills there are no real mules after the switch in notes in 1963. The whole thing about number size was because of the backs from the silver certs being used on the newer fed notes.  Mules listed for 1981 is just found by knowing the plate numbers (no difference in size). They started over with plate 1. So large numbers had to come from 1977a. If your 1981 plate number is a four digit it is from the 1977a series. (ie 3269) Then again on the 1981a series plate numbers above 300 came from the 1981 series.  These are collected as mules but there is no physical difference other that plate numbers that did not exist in that series.  I am sure there are others that could be mules like this but to my knowledge the bep does not give out the plate numbers used for a series. This was only noticed by the large difference. Later on the bep started using a larger back plate number for the fort worth bills. This resulted in the fw 295 plate number error where the back of some bills had the smaller dc plate number 295. This occurred in 1995.

hope this helps. I know this is an old post, I just read it.  This is info i got from other people.