{"id":3735,"date":"2026-11-10T15:34:38","date_gmt":"2026-11-10T07:34:38","guid":{"rendered":"http:\/\/www.nomoreleak.com\/blog\/?p=3735"},"modified":"2026-11-10T15:34:38","modified_gmt":"2026-11-10T07:34:38","slug":"what-is-the-hardness-of-more-o-rings-478f-e8f76c","status":"publish","type":"post","link":"http:\/\/www.nomoreleak.com\/blog\/2026\/11\/10\/what-is-the-hardness-of-more-o-rings-478f-e8f76c\/","title":{"rendered":"What is the hardness of More O Rings?"},"content":{"rendered":"

Hey there, if you\u2019ve ever shopped for O-rings, you\u2019ve probably seen that random number on the packaging or product spec sheet\u2014like 70A, 90 Shore A, or even something lower. As a More O Rings supplier, I get it; most folks ask me way more about size or material than they do about hardness, until something goes wrong. Then suddenly, \u201cWait, why\u2019d this O-ring crush so fast?\u201d or \u201cWhy\u2019s this one leaking when it\u2019s the same size as the last?\u201d That\u2019s almost always tied right to hardness\u2014so today let\u2019s break down what More O Rings hardness actually means, why it matters, and how we (and you) pick the right one for the job. More O Ring<\/a><\/p>\n

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First off, let\u2019s cut through the jargon. When we talk about O-ring hardness, we\u2019re measuring how much the material deforms under pressure\u2014simple as that. The test we use is called the Shore durometer test, and 99% of the time for O-rings, it\u2019s Shore A. There\u2019s Shore D for super-hard plastics, but that\u2019s way too rigid for seals; no one uses that for More O Rings. The scale runs from 0 (super squishy, like a rubber band stretched thin) to 100 (rock hard, like a hockey puck). Most More O Rings we stock land between 60A and 90A, and that range isn\u2019t random\u2014each number serves a purpose.<\/p>\n

Let\u2019s start with the soft end: 60A to 70A. These are your go-to when you need a seal that can squeeze into tiny gaps or conform to rough, uneven surfaces. Think about hydraulic systems where the groove has a few nicks and scratches, or plumbing fittings that aren\u2019t perfectly machined. A soft O-ring will squish into those imperfections, creating a tight seal without forcing you to tighten bolts so much you warp the fitting. I\u2019ve seen a lot of first-time customers reach for a 70A out of habit, but when they tell me their seal\u2019s failing on a worn pump shaft, swapping to a 65A More O Ring fixed it right up. The tradeoff here? They don\u2019t hold up to heavy loads or high pressure as well as harder O-rings. If you\u2019re running 3000 PSI of hydraulic pressure every day, a soft O-ring\u2019s gonna flatten out fast, and that\u2019s a leak waiting to happen.<\/p>\n

Then we\u2019ve got the middle ground, which is the most popular: 75A to 80A. This is the sweet spot for 90% of the applications we deal with\u2014general industrial equipment, automotive components, home appliances, even some aerospace trim seals. It\u2019s firm enough to resist extrusion (that\u2019s when O-ring material gets squeezed into the gaps between mating parts, like a cylinder and its piston) but still pliable enough to install easily. Installing a too-hard O-ring? You can\u2019t stretch it enough to fit over a shaft without nicking it, and if you do force it on, it\u2019ll sit funny in the groove and leak. I had a customer last month who tried to use a 90A More O Ring on a small engine\u2019s valve cover gasket\u2014he snapped two during installation, and the third leaked within a week because it couldn\u2019t conform to the uneven flange surface. Swapping to an 80A fixed it immediately. That\u2019s the thing about the middle range\u2014it\u2019s balanced. If you\u2019re not sure where to start, 75A is our default More O Ring, and we have it in every material (nitrile, EPDM, silicone, Viton) you could need.<\/p>\n

Now the hard end: 85A to 90A. These are for heavy-duty, high-pressure jobs. Think construction equipment hydraulic cylinders, deep well pumps, heavy machinery that runs nonstop 12 hours a day. When you have 5000 PSI pushing on a seal, you need something that won\u2019t squish out of the groove or deform under load. A harder More O Ring here will hold its shape, last longer, and maintain the seal even when temperatures swing wildly or the system has small, sudden pressure spikes. The downside? They\u2019re less forgiving. You can\u2019t use them on rough surfaces, and they\u2019re way more prone to cracking if you stretch them too far during installation. I always make sure to warn customers if their application leans toward 90A\u2014if there\u2019s any chance the groove has sharp edges or the mating parts are a little uneven, we\u2019ll suggest adding a backup ring too, just to be safe.<\/p>\n

Wait, but here\u2019s a thing I see a lot of people mix up: hardness vs. material. Like, a 70A nitrile More O Ring is way different than a 70A silicone O-ring, right? Material affects temperature resistance, chemical compatibility, flexibility at cold temperatures, everything. Hardness is just one variable. For example, silicone More O Rings are naturally softer\u2014most silicone O-rings top out at 80A, because silicone can\u2019t get much harder and still seal. Nitrile (Buna-N) can go all the way up to 90A, which is why it\u2019s so popular for high-pressure hydraulic work. Viton (FKM) is similar to nitrile, great for chemicals and high temperatures, so we stock it from 70A to 90A too. EPDM for water and UV resistance is usually 70A to 80A, since it\u2019s not as rigid as nitrile. So hardness doesn\u2019t tell you what material you have, and material doesn\u2019t tell you the hardness\u2014they\u2019re two separate specs, but they work together.<\/p>\n

Another common question: does hardness change over time? Short answer, yes. That\u2019s called compression set, and it\u2019s a big deal for More O Rings (and all O-rings). If you leave an O-ring compressed in a groove for years, it\u2019ll deform and lose its ability to bounce back\u2014so it gets effectively harder than it was new. That\u2019s why old equipment with original O-rings often leaks, even if you didn\u2019t touch it. We see this all the time with vintage machinery, or even household appliances that haven\u2019t been serviced in a decade. When a customer comes to us with an old dishwasher that\u2019s leaking from the door seal, we ask if they remember the last time they replaced it\u20149 times out of 10, the seal is just compressed and gone hard, so a new More O Ring in the right hardness fixes it.<\/p>\n

What about temperature? Does heat or cold affect hardness? Definitely. When it\u2019s cold, rubber gets stiffer\u2014so a 75A More O Ring that\u2019s soft and pliable at room temp might be 80A or 85A in freezing weather. If you\u2019re running a system in a freezer or a remote cold storage facility, you don\u2019t want to pick an O-ring that gets too hard at low temps\u2014because then it won\u2019t seal when it needs to. On the flip side, high heat softens rubber. A 90A More O Ring that\u2019s firm at room temp might get squishy and deform at 300\u00b0F, which ruins its pressure resistance. That\u2019s why when we help customers pick hardness, we always ask what the operating temperature is, too\u2014we factor that in along with pressure, surface roughness, and application type.<\/p>\n

Let me give you a quick real example, since I always find stories help. Last year, a landscaping equipment dealer came to me because they were having a problem with their new skid steer loaders\u2019 hydraulic cylinders. The O-rings we\u2019d been supplying were 80A, and they were failing within 6 months\u2014leaking, then the cylinder wouldn\u2019t extend. We checked their spec, and turns out their new skid steers run at 5500 PSI, not the 4000 PSI their old models did. The 80A was too soft to hold that pressure long-term, so we swapped them to 90A More O Rings made from nitrile, and now they\u2019re lasting 18+ months, no leaks. That\u2019s exactly why hardness matters\u2014too soft, and it can\u2019t handle the job; too hard, and you\u2019re wasting money on something that\u2019s overkill and harder to install.<\/p>\n

I get that hardness can seem like a tiny, boring detail when you\u2019re ordering O-rings, but it\u2019s one of the biggest factors in whether your seal works for a week or a year. As a More O Rings supplier, my job isn\u2019t just to send you a box of O-rings\u2014it\u2019s to make sure you get the right ones for your specific job. If you\u2019re not sure what hardness you need, just shoot me a note. Tell me what application it\u2019s for, pressure, temperature, what the mating surfaces look like, and I\u2019ll help you pick the perfect More O Ring. No jargon, no hidden fees, just a recommendation that works.<\/p>\n

At the end of the day, O-rings are simple parts, but they make everything from your car to your factory to your dishwasher work. Hardness isn\u2019t just a number on a spec sheet\u2014it\u2019s what keeps your fluid from leaking, your pressure holding, your equipment running. So next time you order O-rings, don\u2019t just look at the size\u2014ask about the hardness, and make sure it matches what you\u2019re doing.<\/p>\n

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If you have questions about More O Rings hardness, need a custom size, or just want to place an order, feel free to reach out to us to connect and discuss your requirements. We\u2019re here to help you get the right seal, every time.<\/p>\n

Rod\/Piston Seal<\/a> References:<\/p>\n

    \n
  1. O-Ring Handbook. Parker Hannifin Corporation, 2021.<\/li>\n
  2. Rubber Durometry Basics. ASTM International, 2019.<\/li>\n
  3. Sealing Technology: Principles and Applications. CRC Press, 2020.<\/li>\n
  4. More O Rings Product Specification Guide. More Sealing Solutions, 2022.<\/li>\n<\/ol>\n
    \n

    Zhejiang Jiacheng New Material Co., Ltd.<\/a>
    Zhejiang Jiacheng New Material Co., Ltd. is one of the most professional more o ring manufacturers and suppliers in China, specialized in providing high quality customized products. We warmly welcome you to buy or wholesale more o ring in stock here from our factory. Contact us for quotation and free sample.
    Address: #64 Anjiang Road, Jianshan New Zone, Huangwan Town, Haining City, Jiaxing City, Zhejiang Province
    E-mail: jcseal_zhu@126.com
    WebSite:     https:\/\/www.sjkseal.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    Hey there, if you\u2019ve ever shopped for O-rings, you\u2019ve probably seen that random number on the … What is the hardness of More O Rings?<\/span>Read more<\/a><\/p>\n","protected":false},"author":18,"featured_media":3735,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3698],"class_list":["post-3735","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-more-o-ring-479f-e92818"],"_links":{"self":[{"href":"http:\/\/www.nomoreleak.com\/blog\/wp-json\/wp\/v2\/posts\/3735","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.nomoreleak.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.nomoreleak.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.nomoreleak.com\/blog\/wp-json\/wp\/v2\/users\/18"}],"replies":[{"embeddable":true,"href":"http:\/\/www.nomoreleak.com\/blog\/wp-json\/wp\/v2\/comments?post=3735"}],"version-history":[{"count":0,"href":"http:\/\/www.nomoreleak.com\/blog\/wp-json\/wp\/v2\/posts\/3735\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.nomoreleak.com\/blog\/wp-json\/wp\/v2\/posts\/3735"}],"wp:attachment":[{"href":"http:\/\/www.nomoreleak.com\/blog\/wp-json\/wp\/v2\/media?parent=3735"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.nomoreleak.com\/blog\/wp-json\/wp\/v2\/categories?post=3735"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.nomoreleak.com\/blog\/wp-json\/wp\/v2\/tags?post=3735"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}