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A question was asked regarding the size for wheel bolts on a Ferrari. I have determine mine to be 14mm diameter x 1.5mm pitch. I was not sure if this was the correct size for other Ferrari's and therefore instructed the respondant to measure his (dino 246). The measurement of the diameter is fairly straight forward but it can be difficult to determine pitch. I suggested the following

A way to tell your pitch

Wrap a piece of paper around an existing clean bolt. Squeeze snuggly and "unscrew the bolt" through your finger pressure. This will make markings on your paper. Using a pencil edge, lightly shade the area to highlight the ridges making them easier to see. Using a metric ruler, count the number of ridges in 1 centimeter. Be as accurate as possible on the last one.

Formula is 10 millimeters / # threads per centimeter = thread pitch

1.0 pitch will have 10 ridges in one centimeter (10 / 10 = 1)

1.5 pitch will have 6.7 lines per centimeter (10 / 6.7 = 1.5)

2.0 pitch will have 5 lines (10 / 5 = 2)

etc...
 

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its even easier than that for metric,

1mm between peaks is 1.0 pitch

1.5mm between peaks is 1.5 pitch and so on...

if it seems like that is too small to determine...its not. the first time you take a steel rule up to a bolt you will immediately realize there is a huge difference between 1mm and even 1.25mm.

1.0-2.0 will be mostly what you encounter in a car, although some interior items or electrical may use 4mm dia. screws that have a 0.8 pitch, while others like the central nut hubs (F40) may be threaded even more coarsly at 2.5 pitch
 

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If any doubt, grab tap and die set. using fingers only die will screw on when pitch and diameter is correct.Takes all guesswork and older eyes out of equation.
 
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