This one is very simple. It's a 3x4" rectangle with some grooves pressed into it by an array of stretched spheres. The grooves are intended to break up an otherwise smooth surface, providing some kind of grip; however, i don't see why this couldn't be printed in whatever material you want.

Printed Dimensions in Woodfil PLA

• Length 101 mm
• Width 76 mm
• Height 2 mm

I've designed a tpu intended, slip-resistant semi-shell to sit this into but I'm not satisfied with it yet.