{"id":15696,"date":"2026-02-26T17:19:00","date_gmt":"2026-02-26T08:19:00","guid":{"rendered":"https:\/\/webstylix.xsrv.jp\/tsr\/?post_type=tips&p=15696"},"modified":"2026-06-28T10:51:05","modified_gmt":"2026-06-28T01:51:05","slug":"blog08","status":"publish","type":"tips","link":"https:\/\/tsrjp.com\/en\/tips\/blog08\/","title":{"rendered":"Bolts That Are Prone to Galling and Bolts That Are Resistant to Galling"},"content":{"rendered":"\n

The phenomenon known as \u201cgalling\u201d in bolts is not caused simply by overtightening or a lack of lubrication.
Whether galling occurs easily or not depends heavily on the combination of materials and the condition of the surfaces involved.<\/p>\n\n\n\n

So why does such a difference occur?
The answer lies in the \u201cinvisible contact\u201d between metals.<\/p>\n\n\n\n

First, let\u2019s take a look at the mechanism behind how galling occurs.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

The Mechanism of Galling<\/h3>\n\n\n\n

When tightening a bolt\u2026<\/p>\n\n\n\n

    \n
  1. The thread surfaces are pressed strongly against each other<\/li>\n\n\n\n
  2. The oxide film on the surfaces breaks down<\/li>\n\n\n\n
  3. Bare metal surfaces come into direct contact<\/li>\n\n\n\n
  4. Localized bonding occurs<\/li>\n\n\n\n
  5. As the bolt continues to turn, those bonded areas are torn apart<\/li>\n\n\n\n
  6. The torn metal transfers to the opposing surface<\/li>\n\n\n\n
  7. The surfaces become rougher and catch even more<\/li>\n\n\n\n
  8. Eventually, the threads lock up (galling)<\/li>\n<\/ol>\n\n\n\n

    In fact, this phenomenon is known as adhesive wear.
    Galling is essentially a process in which metals bond together and those bonded areas are then torn apart.<\/p>\n\n\n\n

    The More Similar the Materials, the Worse It Gets!!<\/h3>\n\n\n\n

    The more similar the materials of the male and female threads are, the higher the likelihood of adhesion occurring.
    In other words, they become much more prone to galling.<\/p>\n\n\n\n

    When the same materials are used together, there is an almost \u201cperfect compatibility\u201d at the atomic level.
    As a result, the moment the oxide film on the surface breaks down, the risk of the metals bonding together (adhesion) increases dramatically.

    Worst Material Combination Rankings<\/p>\n\n\n\n

    \n
    \u30b9\u30af\u30ed\u30fc\u30eb\u3067\u304d\u307e\u3059 <\/i><\/span><\/div>\n
    1st<\/td>Stainless Steel Bolt \u00d7 Stainless Steel Nut<\/td>Maximum Risk!!!<\/td><\/tr>
    2st<\/td>Titanium Bolt \u00d7 Titanium Nut<\/td>Extremely Dangerous!!<\/td><\/tr>
    3st<\/td>Stainless Steel Bolt \u00d7 Titanium Nut<\/td>Pretty Dangerous!<\/td><\/tr>
    Titanium Bolt \u00d7 Stainless Steel Nut<\/td>Prone to Galling Under Normal Use<\/td><\/tr>
    5st<\/td>Aluminum Bolt \u00d7 Aluminum Nut<\/td>May Gall Under Certain Conditions<\/td><\/tr>
    6st<\/td>Titanium Bolt \u00d7 Aluminum Nut<\/td>Aluminum transfers easily.<\/td><\/tr>
    Aluminum Bolt \u00d7 Titanium Nut<\/td>Titanium tends to tear material away.<\/td><\/tr>
    8st<\/td>Stainless Steel Bolt \u00d7 Aluminum Nut<\/td>Caution Level<\/td><\/tr>
    Aluminum Bolt \u00d7 Stainless Steel Nut<\/td>Relatively Better, But\u2026<\/td><\/tr>
    10st<\/td>Iron Bolt \u00d7 Stainless Steel Nut<\/td>Fairly Stable<\/td><\/tr>
    Stainless Steel Bolt \u00d7 Iron Nut<\/td>Iron oxide film helps.<\/td><\/tr>
    12st<\/td>Iron Bolt \u00d7 Iron Nut<\/td>Stable<\/td><\/tr>
    13st<\/td>Iron Bolt \u00d7 Aluminum Nut<\/td>Very Good<\/td><\/tr>
    Aluminum Bolt \u00d7 Iron Nut<\/td>Almost No Problems<\/td><\/tr><\/tbody><\/table><\/figure>\n<\/div>\n<\/div><\/div>\n\n\n\n

    Changing the materials tends to reduce the likelihood of adhesion.
    However, that doesn\u2019t mean any dissimilar combination will work.<\/p>\n\n\n\n

    This is because a different risk called galvanic corrosion arises instead.<\/p>\n\n\n\n

    We explain galvanic corrosion here.<\/p>\n\n\n\n

    \n
    \t\t\t
    \n\t\t\t\t
    \n\t\t\t\t\t\u3042\u308f\u305b\u3066\u8aad\u307f\u305f\u3044<\/span>\n\t\t\t\t\t
    \"\"<\/figure><\/div>\t\t\t\t\t
    \n\t\t\t\t\t\tTitanium helps protect important motorcycles from corrosion.<\/a>\n\t\t\t\t\t\tThe Truth About Titanium, Part 4: \u201cIt doesn\u2019t just resist rust \u2014 it also prevents the other side from rusting.\u201d Most people know that titanium bolts do not r…<\/span>\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t<\/div>\n\t\t<\/div><\/div>\n<\/div><\/div>\n\n\n\n

    Do rolled titanium bolts not gall!?<\/h3>\n\n\n\n

    Titanium is a material that is prone to adhesion.
    There is no doubt that it has a tendency to gall easily.<\/p>\n\n\n\n

    However, this is only true in theory.
    From a manufacturing standpoint, carefully produced rolled titanium bolts rarely gall.<\/p>\n\n\n\n

    At the very least, we have received no reports of galling with our products.
    In fact, off-the-shelf steel or stainless bolts are far more prone to galling.<\/p>\n\n\n

    \n
    \"\"<\/figure>\n<\/div>\n\n\n

    Left: Cut threads,\u3000Right: Rolled threads<\/p>\n\n\n\n

    Through thread rolling, a fiber flow aligned with the thread profile is formed.
    By orienting the metal\u2019s grain structure along the shape, both strength and durability are improved.<\/p>\n\n\n\n

    In addition, work hardening from plastic deformation also occurs.
    As a result, they become about 1.2 to 2 times stronger than cut threads.<\/p>\n\n\n\n

    Also, because titanium is an expensive material, it is not handled as roughly as steel or stainless steel.
    Each piece is carefully finished one by one.<\/p>\n\n\n\n

    A smooth, high-precision surface reduces the microscopic irregularities that can trigger adhesion.
    As a result, the likelihood of galling is significantly reduced.<\/p>\n\n\n\n

    Whether a bolt will gall or not depends heavily on its finish.
    That is the real answer from a manufacturing perspective.<\/p>\n","protected":false},"author":1,"featured_media":17180,"template":"","class_list":["post-15696","tips","type-tips","status-publish","has-post-thumbnail","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/tsrjp.com\/en\/wp-json\/wp\/v2\/tips\/15696","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tsrjp.com\/en\/wp-json\/wp\/v2\/tips"}],"about":[{"href":"https:\/\/tsrjp.com\/en\/wp-json\/wp\/v2\/types\/tips"}],"author":[{"embeddable":true,"href":"https:\/\/tsrjp.com\/en\/wp-json\/wp\/v2\/users\/1"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/tsrjp.com\/en\/wp-json\/wp\/v2\/media\/17180"}],"wp:attachment":[{"href":"https:\/\/tsrjp.com\/en\/wp-json\/wp\/v2\/media?parent=15696"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}