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Geometry/Image Scale and Door Bolt Thickness


Hello sir,

I would like to apologize for the lack of clarity in my previous attempt to ask this question. Now I see that it was difficult to interpret the picture, because the bolts are all retracted. The rear of the door is transparent, which allows you to count 11 horizontal bolts, all made of steel, on each side of the door -- for a total of 22 bolts in all. You can also see that in the recessed section where the door is designed to swing closed, there are 11 holes on each side intended to receive the bolts when extended to lock the door. I have now marked one of the bolts with a red horizontal line.

I have also read that the total thickness of the door itself, from front to back, is three feet (about 91 cm).

Will it now be possible to solve for the approximate bolt diameter? Clearly, every bolt will have the same diameter. I apologize for the fact that I cannot do this work myself.

Once again, thank you very much.

Hi Julian,

Thanks for the clarification.
Looking at the holes on the frame is the more accurate way for me to devise an estimate.  According to the sign above, there is 10'5" of clearance, or 125 inches.  This likely refers to the lowest portion, which is visible at the frame.  (You can see that the front of the door goes up higher than the back.)

The holes appear to be evenly spaced.  Furthermore, the space between holes looks to be of the same size as the holes themselves.  There is also a gap above and below the top and bottom holes, respectively, that are approximately the same size.  This means we can partition the frame into 23 sections, each having the diameter of a hole.

The estimated hole size is therefore 125/23 inches, which is about 5 7/16 inches.  The bolts must have a smaller diameter to fit into the holes, but I imagine they fit it pretty snugly.  I would bring the approximate bolt diameter down to 5 3/8 inches.

Thanks for asking,


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Azeem Hussain


I welcome your questions on algebra, 2D and 3D geometry, parabolic functions and conic sections, and any other mathematical queries you may have.


4 years as a drop-in and by-appointment tutor at Champlain College. Private tutor for dozens of clients over the past 8 years.

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Bachelor of Science, Major Mathematics and Major Economics, McGill University, 2014. Diploma of Collegiate Studies; Pure and Applied Science, Champlain College Saint-Lambert, 2010.

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