Printed mine in PLA .4mm nozzle and .15mm layers, 15% infill.

There are three different designs to choose (plus a blank template). More might come when the inspiration kicks but you can also easily create your own design using the blank-template.stl or the fusion .f3d file provided.

The rings come predefined in three different inner diameters. To fine adjust, though, you can download the finger-surfboard-ring.f3d and in fusion 360 adjust the “dr” user defined parameter to create a ring with your exact fit, which is nicer (and surely way more geeky) than scaling it in the slicer, as it keeps the hole for the string (and all other dimensions like thickness and width) the correct size.

Speaking of the string: I used 2mm paracord, melted the ends with a lighter and pressed them into the countersinks on the surfboard and ring.