A preacher, a lawyer, and an engineer are sentenced to execution...
The preacher is first to be led to the guillotine, and after having his head placed in the stock, the lever is pulled and the blade falls. However, halfway down the blade jams and stops. The preacher looks up and shouts; "it's divine intervention, I must be freed!". The executioner agrees and turns him loose.
The lawyer is next, and after being fitted to the stock, again the deadly lever is pulled. As fate would have it though, the blade again sticks halfway down and after looking up and seeing it, the lawyer shouts; "it's double jeopardy, I must be freed!" Again the executioner agrees and sets the lawyer free.
Finally it's the engineer's turn, and after being set in the stock, yet again the lever is pulled. Remarkably the blade travels halfway way down and stops. The engineer looks up, sees the blade jammed in the frame and says;
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I can fix that for you. 
= new reply since forum marked as read
...to the vertical groove has to be at least 2.5 to 1 for it to slide without binding. If you affix an extension on each side, it'll work just fine. Let me show you."
