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I need to do thread repair (stripped bolt socket in engine block) and buy a kit. For that I need the measurements for my bolt. My question is, how do I obtain those specs when companies nowadays often do not share specs online or are hard to find?

For example, do you do your own measurements of the bolt, like I did here for my Toyota Tacoma timing chain cover:

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I am skeptical about the 7 mm measurement because apparently Toyota does not use that size (even numbers of mm).

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    The easiest way I've found to find the "correct" size is to take it to a hardware store and use their bolt sizer. They usually have a card with several threaded inserts on them. You just keep trying them until you find the one you can screw it into.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Aug 8, 2021 at 23:52
  • I cannot believe there isn't a conversion scale between the actual measurement (like 7 mm here) and whatever they call it for marketing purposes. like 2x4
    – amphibient
    Aug 9, 2021 at 0:27
  • You can also get metric fine and metric coarse threads, so it’s not just the diameter that you need. I would take it to a fastener supplies and get their expert opinion if there was a doubt.
    – HandyHowie
    Aug 9, 2021 at 6:03

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You need a thread pitch gauge to measure the pitch.

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Combine this with the diameter (that you already measured) and the thread length.

The last thing you need is the "bolt grade". There ought to be some markings on the head that indicate the strength of the bolt.

With these informations (diameter, pitch, lentgh and grade) you know all you need to replace the bolt.

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Look like an M7-1.0 bolt to me although you didn't measure the length so that's up to you. The head appears to be 12mm.

Despite what you claim, that Toyota only uses even-sized bolt, that does not appear to be the case.

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  • I agree, but this looks more of a fine thread to me than a 1.0, so best get it checked.
    – HandyHowie
    Aug 9, 2021 at 6:02
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Using a thread pitch gauge is the best way to determine threads. If you can't find a metric pitch gauge then the next best method is using your bolt. Some, not all auto stores stocks nuts and bolts but you can try. Home Depot and other big box stores have nuts and bolts too and you may find sizing info there with your bolt.

Use your bolt and mesh it to another one of the same diameter. When two bolts mesh completely together, you matched threads. incorrect threads won't mesh. Use the size associated with the bolt size, the second number is thread pitch; 1mm, 1.5mm, etc. The first number is the diameter of the bolt threads. You can put your bolt in front or behind the store bolt and see from about two feet away if the store bolt is the same diameter, smaller or larger. Your micrometer caliper is great for measuring diameter. Diameter x thread pitch determines the tap size needed. Then decide if you need a starting tap (tapered) and/or bottom tap (tapping a bind hole).

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