How to Measure a Bolt

  • user warning: Table './tipsformom_drupal/cache_filter' is marked as crashed and should be repaired query: SELECT data, created, headers, expire, serialized FROM cache_filter WHERE cid = '2:41d1ec31e7dcb9df9e08df29253bf140' in /var/www/vhosts/tipsformom.com/httpdocs/includes/cache.inc on line 25.
  • user warning: Table './tipsformom_drupal/cache_filter' is marked as crashed and should be repaired query: UPDATE cache_filter SET data = '<div class=\"mw-parser-output\">\n<p>Figuring out the size of a bolt seems like a simple enough task until you try to match your bolt with a sea of options at the hardware store. In order to get accurate measurements, you’ll need a bolt gauge, which you can purchase from your local hardware or auto parts store. Measure the diameter, thread pitch, and length of the bolt so you can easily find a replacement or matching fasteners.\n</p>\n<h2><span class=\"mw-editsection\"><span class=\"mw-editsection-bracket\">[</span><a target=\"_blank\" href=\"https://www.wikihow.com/index.php?title=Measure-a-Bolt&amp;action=edit&amp;section=1\" title=\"Edit section: Steps\">Edit</a><span class=\"mw-editsection-bracket\">]</span></span><span class=\"mw-headline\" id=\"Steps\">Steps</span></h2>\n<h3><span class=\"mw-editsection\"><span class=\"mw-editsection-bracket\">[</span><a target=\"_blank\" href=\"https://www.wikihow.com/index.php?title=Measure-a-Bolt&amp;action=edit&amp;section=2\" title=\"Edit section: Measuring the Diameter\">Edit</a><span class=\"mw-editsection-bracket\">]</span></span><span class=\"mw-headline\" id=\"Measuring-the-Diameter\">Measuring the Diameter</span></h3>\n<ol>\n<li>Use a bolt gauge to find the diameter quickly and easily. A bolt gauge is divided into standard and metric sections. Usually, the metric holes are in the top row and the standard holes are in the bottom row. Push the bolt into the holes on the gauge and find the smallest hole the bolt will fit into.<sup id=\"_ref-1\" class=\"reference\" aria-label=\"Link to Reference 1\"><a target=\"_blank\" href=\"#_note-1\">[1]</a></sup><br />\n<div class=\"mwimg largeimage floatcenter \" style=\"max-width:728px\"><a target=\"_blank\" href=\"https://www.wikihow.com/Image:Measure-a-Bolt-Step-1-Version-2.jpg\" class=\"image\"><img alt=\"Measure a Bolt Step 1 Version 2.jpg\" src=\"https://www.wikihow.com/images/thumb/7/7d/Measure-a-Bolt-Step-1-Version-2.jpg/aid10556357-v4-728px-Measure-a-Bolt-Step-1-Version-2.jpg\" decoding=\"async\" width=\"728\" height=\"546\" class=\"whcdn\" /></a></div>\n<ul>\n<li>Check more than once to ensure the bolt cannot fit into a smaller hole.</li>\n</ul>\n</li>\n<li>Use a ruler to measure diameter if you don’t have a bolt gauge. Measure from the outermost edge of the bolt’s thread on one side to the outermost edge of the thread on the other side. Make sure your measurement is in a straight line across the thickest portion of the bolt.<sup id=\"_ref-2\" class=\"reference\" aria-label=\"Link to Reference 2\"><a target=\"_blank\" href=\"#_note-2\">[2]</a></sup><br />\n<div class=\"mwimg largeimage floatcenter \" style=\"max-width:728px\"><a target=\"_blank\" href=\"https://www.wikihow.com/Image:Measure-a-Bolt-Step-2-Version-2.jpg\" class=\"image\"><img alt=\"Measure a Bolt Step 2 Version 2.jpg\" src=\"https://www.wikihow.com/images/thumb/1/1f/Measure-a-Bolt-Step-2-Version-2.jpg/aid10556357-v4-728px-Measure-a-Bolt-Step-2-Version-2.jpg\" decoding=\"async\" width=\"728\" height=\"546\" class=\"whcdn\" /></a></div>\n</li>\n<li>Record the diameter. If you used a bolt gauge, make note of the number marked next to the smallest hole the bolt fit through. If you used a ruler, write down the measurements to the nearest millimeter (for metric bolts) or fraction of an inch (for standard bolts).<sup id=\"_ref-3\" class=\"reference\" aria-label=\"Link to Reference 3\"><a target=\"_blank\" href=\"#_note-3\">[3]</a></sup><br />\n<div class=\"mwimg largeimage floatcenter \" style=\"max-width:728px\"><a target=\"_blank\" href=\"https://www.wikihow.com/Image:Measure-a-Bolt-Step-3-Version-2.jpg\" class=\"image\"><img alt=\"Measure a Bolt Step 3 Version 2.jpg\" src=\"https://www.wikihow.com/images/thumb/6/63/Measure-a-Bolt-Step-3-Version-2.jpg/aid10556357-v4-728px-Measure-a-Bolt-Step-3-Version-2.jpg\" decoding=\"async\" width=\"728\" height=\"546\" class=\"whcdn\" /></a></div>\n</li>\n</ol>\n<h3><span class=\"mw-editsection\"><span class=\"mw-editsection-bracket\">[</span><a target=\"_blank\" href=\"https://www.wikihow.com/index.php?title=Measure-a-Bolt&amp;action=edit&amp;section=3\" title=\"Edit section: Finding the Thread Pitch\">Edit</a><span class=\"mw-editsection-bracket\">]</span></span><span class=\"mw-headline\" id=\"Finding-the-Thread-Pitch\">Finding the Thread Pitch</span></h3>\n<ol>\n<li>Turn your bolt gauge over to find the thread gauge. The back of your bolt gauge has plastic ridges that can be used to determine the thread of your bolt. Look at the labels to see which gauge is for standard bolts and which is for metric ones, as they are separate.<sup id=\"_ref-4\" class=\"reference\" aria-label=\"Link to Reference 4\"><a target=\"_blank\" href=\"#_note-4\">[4]</a></sup><br />\n<div class=\"mwimg largeimage floatcenter \" style=\"max-width:728px\"><a target=\"_blank\" href=\"https://www.wikihow.com/Image:Measure-a-Bolt-Step-4-Version-2.jpg\" class=\"image\"><img alt=\"Measure a Bolt Step 4 Version 2.jpg\" src=\"https://www.wikihow.com/images/thumb/1/1d/Measure-a-Bolt-Step-4-Version-2.jpg/aid10556357-v4-728px-Measure-a-Bolt-Step-4-Version-2.jpg\" decoding=\"async\" width=\"728\" height=\"546\" class=\"whcdn\" /></a></div>\n<ul>\n<li>Some thread gauges may look like a pocket knife. If you have one of those, open the thread gauge up by pulling out the first gauge.</li>\n</ul>\n</li>\n<li>Rub the bolt on different sized thread gauges. Run the threads of the bolt along the thread gauge of the appropriate type (standard or metric). Orient the bolt so the threads are facing in the same direction as they are on the gauge. As you rub the bolt on the plastic threads, feel for one that fits correctly.<sup id=\"_ref-5\" class=\"reference\" aria-label=\"Link to Reference 5\"><a target=\"_blank\" href=\"#_note-5\">[5]</a></sup><br />\n<div class=\"mwimg largeimage floatcenter \" style=\"max-width:728px\"><a target=\"_blank\" href=\"https://www.wikihow.com/Image:Measure-a-Bolt-Step-5-Version-2.jpg\" class=\"image\"><img alt=\"Measure a Bolt Step 5 Version 2.jpg\" src=\"https://www.wikihow.com/images/thumb/6/6a/Measure-a-Bolt-Step-5-Version-2.jpg/aid10556357-v4-728px-Measure-a-Bolt-Step-5-Version-2.jpg\" decoding=\"async\" width=\"728\" height=\"546\" class=\"whcdn\" /></a></div>\n<ul>\n<li>If you are using a thread gauge that unfolds like a pocket knife, you’ll need to unfold each gauge and press it up against the threads instead.</li>\n</ul>\n</li>\n<li>Stop when the thread gauge grabs the threads of the bolt. When the plastic threads fit perfectly into the bolt’s threads, you’ve found a match. Look at the gauge from an angle to see if any light passes between the plastic threads and the threads of your bolt. If it does, try the next size down.<sup id=\"_ref-6\" class=\"reference\" aria-label=\"Link to Reference 6\"><a target=\"_blank\" href=\"#_note-6\">[6]</a></sup><br />\n<div class=\"mwimg largeimage floatcenter \" style=\"max-width:728px\"><a target=\"_blank\" href=\"https://www.wikihow.com/Image:Measure-a-Bolt-Step-6-Version-2.jpg\" class=\"image\"><img alt=\"Measure a Bolt Step 6 Version 2.jpg\" src=\"https://www.wikihow.com/images/thumb/9/99/Measure-a-Bolt-Step-6-Version-2.jpg/aid10556357-v4-728px-Measure-a-Bolt-Step-6-Version-2.jpg\" decoding=\"async\" width=\"728\" height=\"546\" class=\"whcdn\" /></a></div>\n<ul>\n<li>Double-check the thread measurement by rubbing the bolt on the gauge a few times. It can be really tough to spot a half millimeter difference in bolt threads, so once you have your thread measurement, do the test one more time to make sure you got the same result.<sup id=\"_ref-7\" class=\"reference\" aria-label=\"Link to Reference 7\"><a target=\"_blank\" href=\"#_note-7\">[7]</a></sup></li>\n</ul>\n</li>\n<li>Make a note of the thread pitch. Once you find the thread that allows no light to pass through, record that measurement. Metric threads are measured in millimeters and are often 1.5 or 2.0 millimeters. Standard threads are counted per inch, so they’re recorded as a single number (like 16).<sup id=\"_ref-8\" class=\"reference\" aria-label=\"Link to Reference 8\"><a target=\"_blank\" href=\"#_note-8\">[8]</a></sup><br />\n<div class=\"mwimg largeimage floatcenter \" style=\"max-width:728px\"><a target=\"_blank\" href=\"https://www.wikihow.com/Image:Measure-a-Bolt-Step-7-Version-2.jpg\" class=\"image\"><img alt=\"Measure a Bolt Step 7 Version 2.jpg\" src=\"https://www.wikihow.com/images/thumb/b/b1/Measure-a-Bolt-Step-7-Version-2.jpg/aid10556357-v4-728px-Measure-a-Bolt-Step-7-Version-2.jpg\" decoding=\"async\" width=\"728\" height=\"546\" class=\"whcdn\" /></a></div>\n</li>\n</ol>\n<h3><span class=\"mw-editsection\"><span class=\"mw-editsection-bracket\">[</span><a target=\"_blank\" href=\"https://www.wikihow.com/index.php?title=Measure-a-Bolt&amp;action=edit&amp;section=4\" title=\"Edit section: Determining the Length\">Edit</a><span class=\"mw-editsection-bracket\">]</span></span><span class=\"mw-headline\" id=\"Determining-the-Length\">Determining the Length</span></h3>\n<p>The bolt\'s length is the distance from the surface of the item being bolted, to the end of the bolt. For a normal hex or pan style bolt, this means the <b>bottom</b> of the head, which will be flush with the surface. For a countersunk bolt, where the top of the head is flush with the surface, the length is measured from the <b>top</b> of the head.\n</p>\n<ol>\n<li>Locate the portion of the bolt’s head which will be flush. On traditional bolts, the flush portion of the head is at the bottom where the head meets the threads of the bolt. On countersunk bolts, which are shaped like cones, the flat portion of the head is the very top.<sup id=\"_ref-9\" class=\"reference\" aria-label=\"Link to Reference 9\"><a target=\"_blank\" href=\"#_note-9\">[9]</a></sup><br />\n<div class=\"mwimg largeimage floatcenter \" style=\"max-width:728px\"><a target=\"_blank\" href=\"https://www.wikihow.com/Image:Measure-a-Bolt-Step-8-Version-2.jpg\" class=\"image\"><img alt=\"Measure a Bolt Step 8 Version 2.jpg\" src=\"https://www.wikihow.com/images/thumb/c/c6/Measure-a-Bolt-Step-8-Version-2.jpg/aid10556357-v4-728px-Measure-a-Bolt-Step-8-Version-2.jpg\" decoding=\"async\" width=\"728\" height=\"546\" class=\"whcdn\" /></a></div>\n</li>\n<li>Measure from the flat portion to the tip of the bolt. Use a ruler or your bolt gauge to measure the length of the bolt starting at the flat portion you identified and ending at the very tip of the bolt’s threaded portion.<sup id=\"_ref-10\" class=\"reference\" aria-label=\"Link to Reference 10\"><a target=\"_blank\" href=\"#_note-10\">[10]</a></sup><br />\n<div class=\"mwimg largeimage floatcenter \" style=\"max-width:728px\"><a target=\"_blank\" href=\"https://www.wikihow.com/Image:Measure-a-Bolt-Step-9-Version-2.jpg\" class=\"image\"><img alt=\"Measure a Bolt Step 9 Version 2.jpg\" src=\"https://www.wikihow.com/images/thumb/8/8d/Measure-a-Bolt-Step-9-Version-2.jpg/aid10556357-v4-728px-Measure-a-Bolt-Step-9-Version-2.jpg\" decoding=\"async\" width=\"728\" height=\"546\" class=\"whcdn\" /></a></div>\n</li>\n<li>Write down the length measurement. For standard bolts, record the measurement to the nearest fraction of an inch. For metric bolts, record the measurement to the nearest millimeter.<sup id=\"_ref-11\" class=\"reference\" aria-label=\"Link to Reference 11\"><a target=\"_blank\" href=\"#_note-11\">[11]</a></sup><br />\n<div class=\"mwimg largeimage floatcenter \" style=\"max-width:728px\"><a target=\"_blank\" href=\"https://www.wikihow.com/Image:Measure-a-Bolt-Step-10-Version-2.jpg\" class=\"image\"><img alt=\"Measure a Bolt Step 10 Version 2.jpg\" src=\"https://www.wikihow.com/images/thumb/1/16/Measure-a-Bolt-Step-10-Version-2.jpg/aid10556357-v4-728px-Measure-a-Bolt-Step-10-Version-2.jpg\" decoding=\"async\" width=\"728\" height=\"546\" class=\"whcdn\" /></a></div>\n</li>\n</ol>\n<h2><span class=\"mw-editsection\"><span class=\"mw-editsection-bracket\">[</span><a target=\"_blank\" href=\"https://www.wikihow.com/index.php?title=Measure-a-Bolt&amp;action=edit&amp;section=5\" title=\"Edit section: Tips\">Edit</a><span class=\"mw-editsection-bracket\">]</span></span><span class=\"mw-headline\" id=\"Tips\">Tips</span></h2>\n<ul>\n<li>Bolt sizes are usually recorded in order as diameter, thread, and length.</li>\n<li>Take your original bolt with you to compare new bolts to when shopping for replacement bolts or fasteners.</li>\n<li>Metric bolts have numbers listed on their heads that indicate their property class. Standard bolts have slashes that indicate the grade of the bolt. Count the slashes and then add 2 to determine the grade.<sup id=\"_ref-12\" class=\"reference\" aria-label=\"Link to Reference 12\"><a target=\"_blank\" href=\"#_note-12\">[12]</a></sup></li>\n<li>Most bolts are “hex” shaped, meaning the head is shaped like a hexagon. However, many bolts come in different head styles for more specific applications. Identify the head style and write it down for when you go shopping for replacement bolts later.<sup id=\"_ref-13\" class=\"reference\" aria-label=\"Link to Reference 13\"><a target=\"_blank\" href=\"#_note-13\">[13]</a></sup></li>\n</ul>\n<h2><span class=\"mw-editsection\"><span class=\"mw-editsection-bracket\">[</span><a target=\"_blank\" href=\"https://www.wikihow.com/index.php?title=Measure-a-Bolt&amp;action=edit&amp;section=6\" title=\"Edit section: Things You’ll Need\">Edit</a><span class=\"mw-editsection-bracket\">]</span></span><span id=\"Things-You’ll-Need\"></span><span class=\"mw-headline\" id=\"Things-You.E2.80.99ll-Need\">Things You’ll Need</span></h2>\n<ul>\n<li>Bolt gauge</li>\n<li>Ruler</li>\n</ul>\n<h2><span class=\"mw-editsection\"><span class=\"mw-editsection-bracket\">[</span><a target=\"_blank\" href=\"https://www.wikihow.com/index.php?title=Measure-a-Bolt&amp;action=edit&amp;section=7\" title=\"Edit section: Related wikiHows\">Edit</a><span class=\"mw-editsection-bracket\">]</span></span><span class=\"mw-headline\" id=\"Related-wikiHows\">Related wikiHows</span></h2>\n<ul>\n<li><a target=\"_blank\" href=\"https://www.wikihow.com/Remove-Rusted-Allen-Bolts\" title=\"Remove Rusted Allen Bolts\">Remove Rusted Allen Bolts</a></li>\n<li><a target=\"_blank\" href=\"https://www.wikihow.com/Remove-a-Broken-Bolt\" title=\"Remove a Broken Bolt\">Remove a Broken Bolt</a></li>\n<li><a target=\"_blank\" href=\"https://www.wikihow.com/Bolt-Into-Concrete\" title=\"Bolt Into Concrete\">Bolt Into Concrete</a></li>\n</ul>\n<h2><span class=\"mw-editsection\"><span class=\"mw-editsection-bracket\">[</span><a target=\"_blank\" href=\"https://www.wikihow.com/index.php?title=Measure-a-Bolt&amp;action=edit&amp;section=8\" title=\"Edit section: References\">Edit</a><span class=\"mw-editsection-bracket\">]</span></span><span class=\"mw-headline\" id=\"References\">References</span></h2>\n<div class=\"mw-references-wrap mw-references-columns\">\n<ol class=\"references\">\n<li id=\"_note-1\"><a target=\"_blank\" href=\"#_ref-1\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"https://youtu.be/uPxHj652Y1w?t=195\">https://youtu.be/uPxHj652Y1w?t=195</a></span>\n</li>\n<li id=\"_note-2\"><a target=\"_blank\" href=\"#_ref-2\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"https://youtu.be/IGfars7Idko?t=69\">https://youtu.be/IGfars7Idko?t=69</a></span>\n</li>\n<li id=\"_note-3\"><a target=\"_blank\" href=\"#_ref-3\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"http://homepages.cae.wisc.edu/~me231/online_notes/dimensoning/fastener_handout.pdf\">http://homepages.cae.wisc.edu/~me231/online_notes/dimensoning/fastener_handout.pdf</a></span>\n</li>\n<li id=\"_note-4\"><a target=\"_blank\" href=\"#_ref-4\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"https://youtu.be/uPxHj652Y1w?t=220\">https://youtu.be/uPxHj652Y1w?t=220</a></span>\n</li>\n<li id=\"_note-5\"><a target=\"_blank\" href=\"#_ref-5\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"https://youtu.be/0JammBOVZ8w?t=277\">https://youtu.be/0JammBOVZ8w?t=277</a></span>\n</li>\n<li id=\"_note-6\"><a target=\"_blank\" href=\"#_ref-6\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"https://youtu.be/0JammBOVZ8w?t=277\">https://youtu.be/0JammBOVZ8w?t=277</a></span>\n</li>\n<li id=\"_note-7\"><a target=\"_blank\" href=\"#_ref-7\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"https://youtu.be/lOoTpbxZQTY?t=49\">https://youtu.be/lOoTpbxZQTY?t=49</a></span>\n</li>\n<li id=\"_note-8\"><a target=\"_blank\" href=\"#_ref-8\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"http://homepages.cae.wisc.edu/~me231/online_notes/dimensoning/fastener_handout.pdf\">http://homepages.cae.wisc.edu/~me231/online_notes/dimensoning/fastener_handout.pdf</a></span>\n</li>\n<li id=\"_note-9\"><a target=\"_blank\" href=\"#_ref-9\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"https://youtu.be/zHZtJ-b75r0?t=42\">https://youtu.be/zHZtJ-b75r0?t=42</a></span>\n</li>\n<li id=\"_note-10\"><a target=\"_blank\" href=\"#_ref-10\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"https://youtu.be/0JammBOVZ8w?t=356\">https://youtu.be/0JammBOVZ8w?t=356</a></span>\n</li>\n<li id=\"_note-11\"><a target=\"_blank\" href=\"#_ref-11\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"http://homepages.cae.wisc.edu/~me231/online_notes/dimensoning/fastener_handout.pdf\">http://homepages.cae.wisc.edu/~me231/online_notes/dimensoning/fastener_handout.pdf</a></span>\n</li>\n<li id=\"_note-12\"><a target=\"_blank\" href=\"#_ref-12\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"https://youtu.be/v2Y28ihPCH8?t=338\">https://youtu.be/v2Y28ihPCH8?t=338</a></span>\n</li>\n<li id=\"_note-13\"><a target=\"_blank\" href=\"#_ref-13\">↑</a> <span class=\"reference-text\"><a target=\"_blank\" rel=\"nofollow noreferrer noopener\" class=\"external free\" href=\"http://homepages.cae.wisc.edu/~me231/online_notes/dimensoning/fastener_handout.pdf\">http://homepages.cae.wisc.edu/~me231/online_notes/dimensoning/fastener_handout.pdf</a></span>\n</li>\n</ol>\n</div>\n</div>\n', created = 1675809736, expire = 1675896136, headers = '', serialized = 0 WHERE cid = '2:41d1ec31e7dcb9df9e08df29253bf140' in /var/www/vhosts/tipsformom.com/httpdocs/includes/cache.inc on line 108.

Figuring out the size of a bolt seems like a simple enough task until you try to match your bolt with a sea of options at the hardware store. In order to get accurate measurements, you’ll need a bolt gauge, which you can purchase from your local hardware or auto parts store. Measure the diameter, thread pitch, and length of the bolt so you can easily find a replacement or matching fasteners.

[Edit]Steps

[Edit]Measuring the Diameter

  1. Use a bolt gauge to find the diameter quickly and easily. A bolt gauge is divided into standard and metric sections. Usually, the metric holes are in the top row and the standard holes are in the bottom row. Push the bolt into the holes on the gauge and find the smallest hole the bolt will fit into.[1]
    Measure a Bolt Step 1 Version 2.jpg
    • Check more than once to ensure the bolt cannot fit into a smaller hole.
  2. Use a ruler to measure diameter if you don’t have a bolt gauge. Measure from the outermost edge of the bolt’s thread on one side to the outermost edge of the thread on the other side. Make sure your measurement is in a straight line across the thickest portion of the bolt.[2]
    Measure a Bolt Step 2 Version 2.jpg
  3. Record the diameter. If you used a bolt gauge, make note of the number marked next to the smallest hole the bolt fit through. If you used a ruler, write down the measurements to the nearest millimeter (for metric bolts) or fraction of an inch (for standard bolts).[3]
    Measure a Bolt Step 3 Version 2.jpg

[Edit]Finding the Thread Pitch

  1. Turn your bolt gauge over to find the thread gauge. The back of your bolt gauge has plastic ridges that can be used to determine the thread of your bolt. Look at the labels to see which gauge is for standard bolts and which is for metric ones, as they are separate.[4]
    Measure a Bolt Step 4 Version 2.jpg
    • Some thread gauges may look like a pocket knife. If you have one of those, open the thread gauge up by pulling out the first gauge.
  2. Rub the bolt on different sized thread gauges. Run the threads of the bolt along the thread gauge of the appropriate type (standard or metric). Orient the bolt so the threads are facing in the same direction as they are on the gauge. As you rub the bolt on the plastic threads, feel for one that fits correctly.[5]
    Measure a Bolt Step 5 Version 2.jpg
    • If you are using a thread gauge that unfolds like a pocket knife, you’ll need to unfold each gauge and press it up against the threads instead.
  3. Stop when the thread gauge grabs the threads of the bolt. When the plastic threads fit perfectly into the bolt’s threads, you’ve found a match. Look at the gauge from an angle to see if any light passes between the plastic threads and the threads of your bolt. If it does, try the next size down.[6]
    Measure a Bolt Step 6 Version 2.jpg
    • Double-check the thread measurement by rubbing the bolt on the gauge a few times. It can be really tough to spot a half millimeter difference in bolt threads, so once you have your thread measurement, do the test one more time to make sure you got the same result.[7]
  4. Make a note of the thread pitch. Once you find the thread that allows no light to pass through, record that measurement. Metric threads are measured in millimeters and are often 1.5 or 2.0 millimeters. Standard threads are counted per inch, so they’re recorded as a single number (like 16).[8]
    Measure a Bolt Step 7 Version 2.jpg

[Edit]Determining the Length

The bolt's length is the distance from the surface of the item being bolted, to the end of the bolt. For a normal hex or pan style bolt, this means the bottom of the head, which will be flush with the surface. For a countersunk bolt, where the top of the head is flush with the surface, the length is measured from the top of the head.

  1. Locate the portion of the bolt’s head which will be flush. On traditional bolts, the flush portion of the head is at the bottom where the head meets the threads of the bolt. On countersunk bolts, which are shaped like cones, the flat portion of the head is the very top.[9]
    Measure a Bolt Step 8 Version 2.jpg
  2. Measure from the flat portion to the tip of the bolt. Use a ruler or your bolt gauge to measure the length of the bolt starting at the flat portion you identified and ending at the very tip of the bolt’s threaded portion.[10]
    Measure a Bolt Step 9 Version 2.jpg
  3. Write down the length measurement. For standard bolts, record the measurement to the nearest fraction of an inch. For metric bolts, record the measurement to the nearest millimeter.[11]
    Measure a Bolt Step 10 Version 2.jpg

[Edit]Tips

  • Bolt sizes are usually recorded in order as diameter, thread, and length.
  • Take your original bolt with you to compare new bolts to when shopping for replacement bolts or fasteners.
  • Metric bolts have numbers listed on their heads that indicate their property class. Standard bolts have slashes that indicate the grade of the bolt. Count the slashes and then add 2 to determine the grade.[12]
  • Most bolts are “hex” shaped, meaning the head is shaped like a hexagon. However, many bolts come in different head styles for more specific applications. Identify the head style and write it down for when you go shopping for replacement bolts later.[13]

[Edit]Things You’ll Need

  • Bolt gauge
  • Ruler

[Edit]Related wikiHows

[Edit]References


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