This is a jig for drilling holes at a 17 degrees angle to get a quick and good joint of wooden boards.  The insert with guide holes was specially designed in OpenSCAD, so you can adjust the hole diameters the way to fit your drill bit (on pic. A) and then generate your own STL file. I suggest you make the guide holes stronger with metal (it may be copper, aluminum, or alloys but iron or steel, no doubt, better) bushings, using tubes of appropriate diameter (as shown on pic. B). The device is also compatible with a jig (see on pic. C) produced by Chinese manufacturers. You'll be able to easily find and purchase it on Amazon or AliExpress for example. To assemble it, you need an M6 x 90 mm bolt, an M6 x 40 mm bolt, an M6 x 18 mm coupling nut, three M6 nuts, an M6 nylon-insert locknut and a washer.  The process of assembly is shown in this tiny video. *https://www.youtube.com/watch?v=Cx5qoVo_p7I* And here's an example of the joint made with the jig.