Normally you can only fit triangular links into a triangle or hexagon shape. Each of these links have been distorted so the pattern will fit nicely into a circle.

Five sizes have been included based on the number of links from the center to the outer edge. Size 3 is good for a typical coaster and Size 1 is useful to quickly check if your printer settings are right.

All the STL files have links that are about 15mm across. The blue pictures show a Size 3 pattern printed at 100% and the black is a Size 5 printed at 60%.

Prusa

i3 MK3

No

No

.15 or .20

none but 3X wall thickness

Keep the retraction below 2mm to keep the feeder from grinding the filament. I have found that for TPU it helps to set the temperature high (235C) to minimize stringing.