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metric bolt thread question


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hello there, so we are planning on putting a different box on the chevrolet 2000 2500 truck, 8 foot bed, i  tried a 7/16ths coarse  thread kind of loose, 1/2 inch to big, so its got to be metric? looks like a 12 mm. size, i see there are 3 different thread pitches for a 12 mm, seeing that the 7/16ths  kind of screws in, i figure it must be the 1.75 pitch, so got a bolt that size , doesnt want to start real easy, also did buy a tap to refresh the threads, question is , what are the metric sizes? what is the next size smaller than the 12 mm. box was from the south so it is in real good shape and all the previous bolts did screw out however the seller did not send along, i also noticed that there are a lot of other metric nuts and bolts on a 20 year old truck, thanks

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Metric has generally more differences than SAE, do you have access to a pitch gauge? What year truck?

Sorry see now 2000

https://spaenaur.com/wp-content/uploads/2018/05/Thread-Size-Comparison-Chart-R8.pdf

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Ream and thread the holes to 1/2, that's what I did when I installed a body lift.

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I would get a metric thread pitch gauge and then go to MCMASTER on line and purchase the correct screw/nut. Most of the GM products were going all metric way back. The pickups were later but by 2000 most were mostly metric.  Some metrics are so close to sae (5/16 / 3/8 / 7/16) that they can easily be confused unless you get the pitch gauge OR MIKE THEM (normally you can go by head marking if they follow DIN specs). Working on old crap today requires a thread pitch gauge!! 

 

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Metric started in the late 70's if I remember right. 

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1 hour ago, SASW6 said:

Metric started in the late 70's if I remember right. 

I was officially educated in 1959 in my general math class. Used it ever since because I am a computer geek, we are all digital/metric.

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Are you talking about the 4 bolts that hold the bed on?  Are they lost or won't transfer over to new bed?  I would think of you had one you could match it.  Just checked Google.  They seem to be out there pretty cheap.

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13 minutes ago, hobbyfarm said:

Are you talking about the 4 bolts that hold the bed on?  Are they lost or won't transfer over to new bed?  I would think of you had one you could match it.  Just checked Google.  They seem to be out there pretty cheap.

He said they were not included in the used bed purchase. My inclination would be to buy the correct bolts for the bed. They are most likely a flange head bolt and possibly a tapered tip if it is like earlier chebbys 

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I buy all my metric nuts & bolts from Belmetric.com   Great website and fast shipping, east coast to west coast typically 2 days. Over $100, I think, free shipping. 

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1 hour ago, bitty said:

He said they were not included in the used bed purchase. My inclination would be to buy the correct bolts for the bed. They are most likely a flange head bolt and possibly a tapered tip if it is like earlier chebbys 

Was just wondering if whatever bed was on there 1st had bolts that could be reused.  Not really a mechanic or fabricator like some of you Incredible guys but do remember when I took the bed off my 2002 it had the tappered tip flange bolt you describe.

Other thought is a junkyard close by but clicking online to get new ones on your doorstep sure is convienant. 

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Metric is french from....1700s and the normalized in 1800s in most of europe.

Frankly, besides bolts, it makes more sense.  PT my 1994 chev has alot of metric on it you 2000 is all metric iirc.  

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Hello , thanks for  the replies, it might be like Bitty has said tapered bolt, i have seen them on other parts of truck, might explain why the regular bolt that i try wont start, anyway did get 12 by 1.75 tap will try that first, and you are right about bolt kit, napa has the 8 bolt set for 20 bucks, thanks again!

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well besides everything else that is going on lately, i did get a chance to run a 1.75 by 12 mm. tap up the holes and it worked good. still wondering why the bolt that i bought wouldnt start, maybe it does take that tapered bolt like bitty suggested, thanks by the way we sure are experiencing some really nice weather here in central wis. the last week and looks to be even warmer next week, a 70 degree difference

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