This handle adds an extension to the small handle of the Lee Automatic Processing Press (APP,) and really increases the comfort and speed of the press. To mount the handle, I replaced the existing bolt and nut using a 1/4-20 x 4" bolt from Lowe's (threaded portion 1"/~25mm not threaded all the way up,) two washers, regular nut, locknut filler, and a nylon lock nut. I had to extend the threaded portion about 1/4" (about 6.5mm) to get enough thread for the lock nut to get a good bite. I've made this with PLA and PETG and they both seem to work fine. Assembly is straight forward. A washer goes against the bolt's hex head, the bolt is slipped in the outer portion of the handle, a second washer and bolt are tightened to the end of the thread, then inserted through the Lee handles where the locknut filler and lock-nut are tightened. The trick is to have just enough play between the handle and two washers so it spins freely. A little grease certainly helps to keep it rolling smoothly. It is, of course ambidextrous, so put it on whichever side you want. I found the most support and comfort came from keeping my thumb and forefinger around the Lee handle, and the rest of my hand on the extension. I included the SCAD so you can tweak this to fit your hand.
Update. I added a small 7/16" wrench to hold the bolt in the handle while tightening the lock nut.

Creality

Ender 3

No

Yes

.25

20%

I printed the "inside" of the handle down (the part that goes into the Lee handle.) I used a brim to get better adhesion, and supports in the center.