... now have the keys: 2_011237_190000000.png I have modified the prototype by providing a taper clearance from the rail web at each end, with only a short central pad area in firm contact with the rail web. This should ease problems with threading rail through, and reduce stress on the chair. The amount of taper clearance and the width of the centre pad are adjustable for best results. Or by setting the clearance to zero you can revert to the normal prototype design. It is easier to see without the rail in place: 2_011241_550000000.png The end clearance is visible here at A: 2_011242_350000000.png The remaining dimensions of the key are taken from the entered rail section dimensions. The keys can be set for left or right hand drive, and the amount of key remaining projecting is random for each key. You can see that in this side-on view: 2_011244_220000000.png It would all look more intelligible with the chair jaws in place, so that's the next job. In the meantime, I think I will have a nice boiled egg. Martin. posted: ...