These pulleys are acetal (engineer plastic), there are no need to overtighten. I also did not tap the pulleys all the way thru so when you thread in the bolts, you will encounter resistance at the end point which also lock the bolt in place, like a lock nut but without one.
Is there any benfits to use POM instead of aluminium? I would guess the aluminium are stronger?
Check out this link: http://www.productiveplastics.com/metal-vs-plastic-5-key-comparisons/ and other countless info you could find about modern plastics and their capabilities.
That would be great indeed. Every DIY pulley I’ve seen so far that didn’t have a lip or interface wobbles like an egg.
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Lip is available as an option 
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What I have experienced is that my nylon 3D printed pulleys have outlasted my aluminum pulleys. But, that is just my experience.
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Thats interesting. What type of nylon was used, Taulman 910 or?
This is what I use: http://www.microcenter.com/product/485160/175mm_Natural_Nylon_3d_Printer_Filament_-05kg_Spool(11_lbs) I also recently tried the Gizmo Dorks nylon filament. At the same settings, the layers would not adhere.
Contact point with the thane and pulley is increased by extended flange. Optional lip can also be added for small size pulley
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Pulleys for MBS 100mm
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I’ll be the test pilot for those babies. 
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Has anyone buy one to try out? Really interested in this but not sure how many to get yet.
I personally dont like them. I bought a set of 35t for kegels. It presses against a lot of thane on both sides. Very difficult to properly align and requires filing for caliber 2 trucks.
The newly modified pulleys have a larger bore hole to clear the truck’s hanger. The pulleys are design to sit on the thane, it’s not necessary to overly tighten the bolts. Not sure what you meant by difficulty in aligning the pulley, I tested them on TB, Caliber, Paris with ABEC, Kegal, MBS, and clones, they went in with ease.
Hmm I wonder why people make bolt through pulleys when slide in pullies are so easy to change gear ratios on the fly or just change your wheels no mucking about required.
I have 3d printed 33t pullies from @longhairedboy that get my board to 44mph and I’m currently running old Enertion stock of the 36t slip on pullies.
If you make slip on pullies then I’ll buy more of the cause changing gear ratios can be fun.
Bolt through left. Slip on right. For illistration purposes.
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Please forgive my possibly noonish question: is it bad to have the pulley press against the thane?
I don’t know why the big fuss about pulley pressing against the thane. The whole circumference of the pulley is evenly laid on the thane which distributed the pulling force around it when you tighten the bolts.
having slip on pulleys minimize installation time but again, how often do you really change out gear ratio? To machine slip on pulleys is not difficult but require building different fixture and jigs for work-holding which translate to $$$.
These pulleys are designed in CAD for specific type of wheels and machine on CNC mill with much higher tolerance than you ever need for esk8 parts. Alignment would not be an issue.
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Well because the urathane compresses on the bottom and more so when cornering and since the pully is resting on the thane it puts alot of stress on the pullies. It may be fine but people are unwilling to risk their bodies on something they know is not right.