{"title":"Forespar Marelon Thru-Hulls — Understanding Threadforms","description":"\u003clink rel=\"stylesheet\" href=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0879\/4908\/2930\/files\/om-manual-v2.css\"\u003e\u003cstyle\u003e.mpom .om-tbl.nw td+td{white-space:nowrap}.mpom details.om-dd{position:relative;margin:0}.mpom details.om-dd\u003esummary{list-style:none;cursor:pointer}.mpom details.om-dd\u003esummary::-webkit-details-marker{display:none}.mpom .om-dd-menu{position:absolute;left:0;top:calc(100% + 6px);min-width:100%;width:max-content;max-width:360px;background:#fff;border:1px solid #e3e5e8;border-radius:6px;box-shadow:0 8px 24px rgba(0,0,0,.14);z-index:30;padding:6px}.mpom .om-dd-menu a{display:flex;justify-content:space-between;align-items:center;gap:14px;padding:10px 12px;border-radius:4px;font-size:14px;font-weight:600;color:#2a2b2a!important;text-decoration:none!important}.mpom .om-dd-menu a:hover{background:#f5f6f8}.mpom .om-dd-menu small{font-weight:400;color:#5f6368;white-space:nowrap}\u003c\/style\u003e\u003cdiv class=\"mpom\"\u003e\n\u003cdiv class=\"om-head\"\u003e\n\u003cdiv\u003e\n\u003cspan class=\"om-tag\"\u003eINSTRUCTIONS\u003c\/span\u003e\u003cp class=\"om-lead\"\u003eMatch threads correctly when joining Forespar Marelon thru-hulls, valves and tailpipes to bronze, stainless or PVC fittings – NPT vs parallel vs BSP – with the BSP part-number cross-reference.\u003c\/p\u003e\n\u003cdiv class=\"om-box\"\u003e\n\u003cdiv class=\"om-row\"\u003e\n\u003cspan\u003eDocument\u003c\/span\u003e\u003cb\u003eForespar Marelon Thru-Hulls Understanding Threadforms\u003c\/b\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"om-row\"\u003e\n\u003cspan\u003eFormat\u003c\/span\u003e\u003cb\u003ePDF · 2 pages · 0.2 MB\u003c\/b\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"om-row\" style=\"border-bottom:0\"\u003e\n\u003cspan\u003eLanguage\u003c\/span\u003e\u003cb\u003eEnglish\u003c\/b\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"om-acts\"\u003e\n\u003cdetails class=\"om-dd\"\u003e\u003csummary class=\"om-btn dl\"\u003e\u003csvg viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2.4\" stroke-linecap=\"round\" stroke-linejoin=\"round\"\u003e\u003cpath d=\"M12 4v11\"\u003e\u003c\/path\u003e\u003cpath d=\"m7 10 5 5 5-5\"\u003e\u003c\/path\u003e\u003cpath d=\"M5 20h14\"\u003e\u003c\/path\u003e\u003c\/svg\u003e Download PDF ▾\u003c\/summary\u003e\u003cdiv class=\"om-dd-menu\"\u003e\n\u003ca href=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0879\/4908\/2930\/files\/Forespar-Marelon-Understanding-Threadforms-Tech-Tips.pdf\" target=\"_blank\" rel=\"noopener\"\u003e\u003cspan\u003eInstructions\u003c\/span\u003e\u003csmall\u003ePDF · 2 p.\u003c\/small\u003e\u003c\/a\u003e\u003ca href=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0879\/4908\/2930\/files\/Forespar-Marelon-Valves-on-Bronze-Thru-Hulls-Tech-Tips.pdf\" target=\"_blank\" rel=\"noopener\"\u003e\u003cspan\u003eMarelon valves on bronze thru-hulls (M4)\u003c\/span\u003e\u003csmall\u003ePDF · 1 p.\u003c\/small\u003e\u003c\/a\u003e\u003ca href=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0879\/4908\/2930\/files\/Forespar-Marelon-Series-93-NPT-Parallel-Threads-Tech-Tips.pdf\" target=\"_blank\" rel=\"noopener\"\u003e\u003cspan\u003eSeries 93 NPT parallel threads (M22)\u003c\/span\u003e\u003csmall\u003ePDF · 1 p.\u003c\/small\u003e\u003c\/a\u003e\n\u003c\/div\u003e\u003c\/details\u003e\u003ca class=\"om-btn buy\" href=\"\/collections\/forespar-sailboat-marine-plumbing\"\u003eView Collection\u003c\/a\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"om-toc\"\u003e\n\u003ca href=\"#om-threads\"\u003eThread Forms\u003c\/a\u003e\u003ca href=\"#om-bsp\"\u003eBSP Cross-Reference\u003c\/a\u003e\u003ca href=\"#om-bronze\"\u003eOn Bronze Thru-Hulls\u003c\/a\u003e\u003ca href=\"#om-93\"\u003eSeries 93 NPSM\u003c\/a\u003e\u003ca href=\"#om-products\"\u003eProducts\u003c\/a\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"om-img\"\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0879\/4908\/2930\/files\/Forespar-Marelon-Understanding-Threadforms-Tech-Tips-Cover.png\" alt=\"Forespar Marelon Thru-Hulls — Understanding Threadforms\" loading=\"lazy\"\u003e\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"om-block\" id=\"om-threads\"\u003e\n\u003ch2 class=\"om-h\"\u003eUnderstanding Threadforms (M6)\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eAll Marelon thru-hulls have parallel threads: \"NPT\" style but not tapered. No thru-hulls, of any material, have tapered threads. The parallel form is called NPSM (American Standard Straight Mechanical Pipe Thread) or NPSC (Straight Coupling Pipe Thread) – basically the same.\u003c\/li\u003e\n\u003cli\u003ePlastic injection-moulded thread forms are made to ANSI B2.1 and SAE J476.\u003c\/li\u003e\n\u003cli\u003eNPT (American Standard Pipe Taper Thread) is the standard for industrial and household pipe fittings; its end threads are deliberately imperfect to seal as the joint tightens.\u003c\/li\u003e\n\u003cli\u003eMarelon valves, elbows and tailpipes have parallel threads matching the thru-hulls. None of these is self-sealing: use pipe dope, thread-seal compound or Teflon tape on all Marelon plumbing fittings.\u003c\/li\u003e\n\u003cli\u003eA tapered male thread will screw into a Marelon female thread, but the connection may be weak and harder to seal. A male Marelon fitting (or a male metal fitting) will not work in a female tapered thread.\u003c\/li\u003e\n\u003cli\u003eCross-threading or mismatched threads can cause leaks and failure of the connection.\u003c\/li\u003e\n\u003cli\u003eThread angle: British BSP 55°, American NPT 60°.\u003c\/li\u003e\n\u003cli\u003eNPT tapered male tailpipes are offered in some sizes (model \"HC\", numbers 910146 thru 910168, page 8 of the Marelon Plumbing Systems Catalog). BSP threads are available on some fittings.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"om-block\" id=\"om-bsp\"\u003e\n\u003ch2 class=\"om-h\"\u003eBSP – British Standard Pipe Versions\u003c\/h2\u003e\n\u003cdiv class=\"om-tbl nw\"\u003e\u003ctable\u003e\n\u003ctr\u003e\n\u003cth\u003ePart # (standard)\u003c\/th\u003e\n\u003cth\u003eDescription\u003c\/th\u003e\n\u003cth\u003eBSP part #\u003c\/th\u003e\n\u003cth\u003e\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e901008\u003c\/td\u003e\n\u003ctd\u003eHECF 16 elbow, 1\" female\u003c\/td\u003e\n\u003ctd\u003e901017\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e901009\u003c\/td\u003e\n\u003ctd\u003eHECF 20 elbow, 1-1\/4\" female\u003c\/td\u003e\n\u003ctd\u003e901018\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e901010\u003c\/td\u003e\n\u003ctd\u003eHECF 24 elbow, 1-1\/2\" female\u003c\/td\u003e\n\u003ctd\u003e901019\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e901011\u003c\/td\u003e\n\u003ctd\u003eHECF 32 elbow, 2\" female\u003c\/td\u003e\n\u003ctd\u003e901020\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e901002\u003c\/td\u003e\n\u003ctd\u003eHECM 16 elbow, 1\" male\u003c\/td\u003e\n\u003ctd\u003e901021\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e901003\u003c\/td\u003e\n\u003ctd\u003eHECM 20 elbow, 1-1\/4\" male\u003c\/td\u003e\n\u003ctd\u003e901022\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e901004\u003c\/td\u003e\n\u003ctd\u003eHECM 24 elbow, 1-1\/2\" male\u003c\/td\u003e\n\u003ctd\u003e901023\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e901005\u003c\/td\u003e\n\u003ctd\u003eHECM 32 elbow, 2\" male\u003c\/td\u003e\n\u003ctd\u003e901024\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e906004\u003c\/td\u003e\n\u003ctd\u003eCF 250 1\" thru-hull\u003c\/td\u003e\n\u003ctd\u003e901025\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e906008\u003c\/td\u003e\n\u003ctd\u003eCF 250 1-1\/2\" thru-hull\u003c\/td\u003e\n\u003ctd\u003e901026\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e906014\u003c\/td\u003e\n\u003ctd\u003eCF 251 1\" thru-hull\u003c\/td\u003e\n\u003ctd\u003e901027\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e906016\u003c\/td\u003e\n\u003ctd\u003eCF 251 1-1\/4\" thru-hull\u003c\/td\u003e\n\u003ctd\u003e901028\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e906018\u003c\/td\u003e\n\u003ctd\u003eCF 251 1-1\/2\" thru-hull\u003c\/td\u003e\n\u003ctd\u003e901029\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e906020\u003c\/td\u003e\n\u003ctd\u003eCF 251 2\" thru-hull\u003c\/td\u003e\n\u003ctd\u003e901030\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e905008\u003c\/td\u003e\n\u003ctd\u003eCF 252 1\" tailpipe\u003c\/td\u003e\n\u003ctd\u003e901032\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e905009\u003c\/td\u003e\n\u003ctd\u003eCF 252 1-1\/4\" tailpipe\u003c\/td\u003e\n\u003ctd\u003e901033\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e905010\u003c\/td\u003e\n\u003ctd\u003eCF 252 1-1\/2\" tailpipe\u003c\/td\u003e\n\u003ctd\u003e901034\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e905011\u003c\/td\u003e\n\u003ctd\u003eCF 252 2\" tailpipe\u003c\/td\u003e\n\u003ctd\u003e901035\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e905102\u003c\/td\u003e\n\u003ctd\u003eMF 850 1\" PTFE ball valve\u003c\/td\u003e\n\u003ctd\u003e901036\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e905103\u003c\/td\u003e\n\u003ctd\u003eMF 850 S 1-1\/4\" PTFE ball valve\u003c\/td\u003e\n\u003ctd\u003e901037\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e905104\u003c\/td\u003e\n\u003ctd\u003eMF 850 1-1\/2\" PTFE ball valve\u003c\/td\u003e\n\u003ctd\u003e901038\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e905105\u003c\/td\u003e\n\u003ctd\u003eMF 850 2\" PTFE ball valve\u003c\/td\u003e\n\u003ctd\u003e901039\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e906066\u003c\/td\u003e\n\u003ctd\u003eMF 810 water strainer\u003c\/td\u003e\n\u003ctd\u003e906068\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e910063\u003c\/td\u003e\n\u003ctd\u003eRB 24-12\u003c\/td\u003e\n\u003ctd\u003e910180\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e907009\u003c\/td\u003e\n\u003ctd\u003eCF 249 1\" thru-hull nut\u003c\/td\u003e\n\u003ctd\u003e920380\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e907010\u003c\/td\u003e\n\u003ctd\u003eCF 249 1-1\/4\" thru-hull nut\u003c\/td\u003e\n\u003ctd\u003e920381\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e907011\u003c\/td\u003e\n\u003ctd\u003eCF 249 1-1\/2\" thru-hull nut\u003c\/td\u003e\n\u003ctd\u003e920382\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e907012\u003c\/td\u003e\n\u003ctd\u003eCF 249 2\" thru-hull nut\u003c\/td\u003e\n\u003ctd\u003e920383\u003c\/td\u003e\n\u003ctd\u003e\u003ca class=\"om-ask\" href=\"\/pages\/contact\"\u003eAsk us to source it →\u003c\/a\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/table\u003e\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"om-block\" id=\"om-bronze\"\u003e\n\u003ch2 class=\"om-h\"\u003eMarelon Valves on Bronze Thru-Hulls (M4)\u003c\/h2\u003e\n\u003cp\u003eReplacing only the valve on a sound existing thru-hull is common practice. MF 850 and MF 849 ball valves, and \"93\" Series integrated valves, are installed on bronze (and stainless) thru-hulls.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eBe sure the bronze thru-hull is sound (no electrolysis or corrosion damage).\u003c\/li\u003e\n\u003cli\u003eClean the threads and remove all old sealant.\u003c\/li\u003e\n\u003cli\u003eDo not cross-thread: bronze will \"cut\" threads if forced onto Marelon.\u003c\/li\u003e\n\u003cli\u003eUse adequate Teflon pipe tape or plumber's dope as thread sealant.\u003c\/li\u003e\n\u003cli\u003eDo not disturb the sealant on the thru-hull by twisting it in the hull.\u003c\/li\u003e\n\u003cli\u003eDo not over-tighten the valve: hand tight is all that is needed.\u003c\/li\u003e\n\u003cli\u003eBond or ground the bronze thru-hull properly: it is still subject to electrolysis and corrosion with a Marelon valve on it.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp class=\"om-note\"\u003eForespar cannot guarantee thread compatibility with some foreign-made bronze thru-hulls.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"om-block\" id=\"om-93\"\u003e\n\u003ch2 class=\"om-h\"\u003eSeries 93 NPT Parallel Threads (M22)\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eMarelon NPT-parallel (NPSM) threaded flanged seacocks accept bronze or stainless steel thru-hulls.\u003c\/li\u003e\n\u003cli\u003eABYC \/ U.L. approved for below the waterline.\u003c\/li\u003e\n\u003cli\u003eMultiple port valves ½\" thru 2\"; valve locks available on 1\" thru 2\".\u003c\/li\u003e\n\u003cli\u003eMarelon valves do not require bonding.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cp class=\"om-note\"\u003eNeed a part that isn't listed? \u003ca href=\"\/pages\/contact\"\u003eAsk us to source it\u003c\/a\u003e and quote the part number from the PDF.\u003c\/p\u003e\n\u003ch2 class=\"om-h\" id=\"om-products\"\u003eProducts in this Manual\u003c\/h2\u003e\n\u003c\/div\u003e","products":[],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0879\/4908\/2930\/collections\/Forespar-Marelon-Understanding-Threadforms-Tech-Tips-Cover.png?v=1793136459","url":"https:\/\/www.mauripro.com\/collections\/owners-manuals-forespar-marelon-thru-hull-threadforms.oembed","provider":"MAURIPRO Sailing","version":"1.0","type":"link"}