I suggest this combo:
-Screw Clamp.stl         (Hex or not, your choice)
-Insert1mm8.5mm.stl
-Clamp Nut3.5mm.stl  (Hex or not, your choice)
(The original was "Insert1mm8.2mm"-"Clamp Nut1.5mm")
This tapered thread bowden coupling is made to improve the original one (made in brass with weak grip) by putting a case on it.
The M6 thread can be tightened really good.
This is my second version. This thing was made with Solidworks which mean you can modify it or request a modification!
First version: https://www.thingiverse.com/thing:3592750
Inspiration: https://www.thingiverse.com/thing:1993384
Edit (V2.1) 2019-11-25:
Made some tolerance for the "Insert","Screw Clamp" and the "Clamp Nut" based on the reviews of Haazaboge; Bubble_Guy; jhillyerd; gromi. Thanks for the comments, it really help!

This remix will work for every one since the threads are from the real PC4 fitting.
You need to dismount the PC4 fitting using a pliers get the top plastic over, them using a little screwdriver get the inside metal and plastics out.
Now print this remix and use a superglue on the sides of the nut and insert the PC4 into the thing and let it dry.
UPDATE: If you use the effector bellow:
(https://pt.aliexpress.com/item/3D-Printer-Accessories-Aluminum-Metal-M3-Delta-Kossel-Fisheye-Effector-Hanging-Station-with-Mounting-Plate-for/32823288982.html?spm=a2g03.search0204.3.51.72c2f74dh1n5Vx&ws_ab_test=searchweb0_0,searchweb201602_1_10065_10068_10547_10059_10884_10548_10887_10696_100031_10084_5711611_10083_10103_10618_10307,searchweb201603_45,ppcSwitch_5_ppcChannel&algo_expid=c6de737b-992e-4a6f-83de-1f36daccf577-6&algo_pvid=c6de737b-992e-4a6f-83de-1f36daccf577&priceBeautifyAB=0
You can left the bottom piece of the effector out and use this thing to keep the heatsink block in place without ANY SCREW !!! It works really…