Summary This is one of those tools you wonder what you did without it, it is so simple. The number of times I have had to trace along a piece of track to mark out where I want to lay the underlay, or marking out the curved form-work to lay the track. Of course one does not have a set of radius curves of every size so this simple device joined up with the OO/HO FLEXITRACK CURVE FORMING CLAMPS in http://www.thingiverse.com/thing:2023001 you can make a radius template any size you like, and is not limited to model railways uses either.