I've modded the original with right hand filament cooler so the magnets I've lying around from my R/C hobby will fit.
The magnets are 6mm round shims and 2.9mm thick
Here is a link to the magnets I've used and that fit really perfect:
However, I didn't reduce the diameter of the original magnet mounting holes, so 1/4" magnets will also fit well
By request I've added a version with a 7mm lowered mount called "30mm_wnn_exotic.stl"
and one with an 8mm lowered mount that I think should work with an E3Dv6 with "VOLCANO" heater.
I have a "VOLCANO" lying around but not installed, so let me know if it works well for you.
Added a part called: "for clearance adjustment", if you have trouble with the clearance of the joint just ungroup the parts, stretch the insert to the size you need , slip it in place and cut it out with the .stl editor of your choice.
The most ease to do that is the free 3D Builder from MS what comes with should come with your if you use win10.
Anet A8 B with E3D v6 bowden and RAMPS 1.4
I've printed the combo with white ABS with Brim and it came out very well, lying in the fan side the 40mm doesn't need any support and the 30mm only under the magnet mount.
The 30mm fits really well and tight on the E3D v6 and caused by the little nose, the magnet mount need only one pair of magnets in the lower position.
The weight of my ABS combo is 15 gr. without magnets and fans.
The complete thing with magnets, both fans and a small 3 LED bracket weights 44gr.