The MSE reply is mathematically appropriate, acceptable for that web site. However the puzzle on this web site simply asks for a nonagon that’s “a part of” strips a few unit vast. A a lot easier reply matches 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 an everyday nonagon. Make 2 extra of those. Join the ends of the arms to get a barely irregular nonagon. The vertices of an everyday 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, in all probability throughout the radius of the bolt and undoubtedly “a part of” the strips.
To satisfy 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.)