Help idenitifying bolt size

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  #1  
Old 10-31-18, 01:14 PM
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Help idenitifying bolt size

I need to determine the size of a particular bolt in order to purchase the proper tap. I thought it was a 12MM bolt, but I am measuring 12.5MM with my caliper. Thread pitch is 1.25MM. Is 12.5MM outside the acceptable tolerance for the nominal diameter of this size bolt? 12MM is close to 1/2" and 1.25MM thread pitch is about 20/inch, but 1/2-20 is not a standard size. This is off a child's bicycle, most definitely made in China, so maybe it's some odd ball size?
 
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Old 10-31-18, 01:22 PM
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Do you have a hardware store nearby that has a metric thread gauge ?
 
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Old 10-31-18, 01:43 PM
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Do you have a hardware store nearby that has a metric thread gauge?
I measured the thread pitch with a gauge and got 1.25MM. Are you talking about the kind you can screw bolts into to check if it threads in properly?
 
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Old 10-31-18, 01:58 PM
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Yes . . . . full service hardware stores will often have exposed metric nut and bolt threads for most popular sizes and pitches for their Customers to use before finalizing a sale.
 
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Old 10-31-18, 02:00 PM
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Yes . . . . full service hardware stores will often have exposed metric nut and bolt threads for most popular sizes and pitches for their Customers to use before finalizing a sale.
Yes, they have one of those. I'll swing by this weekend. Thanks.
 
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Old 10-31-18, 03:12 PM
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1/2- 20 is a standard SAE fine thread.
 
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Old 11-01-18, 08:09 AM
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1/2- 20 is a standard SAE fine thread.
Hmm, okay. Maybe that's what I have then, because 12.5mm seems way out of acceptable tolerance for a 12mm bolt, don't you agree? Whereas I believe 0.492" is within acceptable tolerance for a 1/2" bolt.
 
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Old 11-06-18, 10:38 AM
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It's a 1/2-20 as suggested. I was able to clean up the threads on the bike pedals using a 1/2-20 RH and LH nut and purchased 1/2-20 LH and RH taps to clean up the threads on the bike. All is good now
 
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