The MSE reply is mathematically right, acceptable for that website. But the puzzle on this website simply asks for a nonagon that’s “a part of” strips a couple of unit large. A a lot easier reply suits that criterion, based mostly on triangles with sides of 4,4, and 6 items

Bolt the ends of two 10-unit strips collectively, then bolt two holes six items aside on one other strip to holes 4 items from that hinge. (I used the holes 2 items in from the ends of one other 10-strip within the determine beneath.) This provides a 4,4,6 triangle with inflexible 6-unit extensions at an angle near the 140 levels in a daily nonagon. Make 2 extra of those. Connect the ends of the arms to get a barely irregular nonagon. The vertices of a daily nonagon, proven in black, are inside about 1/9 of a unit (~0.11115916 items to be extra exact) of the middle of the bolts, most likely throughout the radius of the bolt and positively “a part of” the strips.

To meet the second criterion, join the additional ends of every strip used for the lengthy facet of a triangle to 2 18- or 19-unit strips and join the opposite ends of these strips to one another. (I used two 18-units strips within the determine.)