{"id":855,"date":"2026-08-07T17:43:43","date_gmt":"2026-08-07T15:43:43","guid":{"rendered":"https:\/\/fixwoodsystem.pl\/guides\/full-or-partial-thread\/"},"modified":"2026-10-12T14:28:46","modified_gmt":"2026-10-12T12:28:46","slug":"full-or-partial-thread","status":"publish","type":"page","link":"https:\/\/fixwoodsystem.pl\/en\/guides\/full-or-partial-thread\/","title":{"rendered":"Full thread or partial thread - which and when"},"content":{"rendered":"<p class=\"lead\">The capacity of a joint is decided by diameter, penetration length, timber density and driving angle. The thread type is chosen by how the joint has to work - and that is the question most commonly confused of them all. It is not about which thread is &#8220;stronger&#8221; - it is about which job it has to do.<\/p>\n<nav class=\"fws-spis\" aria-labelledby=\"fws-spis-tytul\">\n<p class=\"fws-spis-tytul\" id=\"fws-spis-tytul\">Contents (13 sections)<\/p>\n<ol>\n<li><a href=\"#the-difference-is-mechanical-not-marketing\">The difference is mechanical, not marketing<\/a><\/li>\n<li><a href=\"#where-the-weak-link-sits\">Where the weak link sits<\/a><\/li>\n<li><a href=\"#the-third-variant-dual-zone-thread\">The third variant: dual-zone thread<\/a><\/li>\n<li><a href=\"#how-to-choose\">How to choose<\/a><\/li>\n<li><a href=\"#why-full-stronger-is-a-bad-shortcut\">Why &#8220;full = stronger&#8221; is a bad shortcut<\/a><\/li>\n<li><a href=\"#the-common-mistake-and-what-it-looks-like\">The common mistake and what it looks like<\/a><\/li>\n<li><a href=\"#cross-grain-reinforcement-where-it-really-shows\">Cross-grain reinforcement - where it really shows<\/a><\/li>\n<li><a href=\"#what-happens-while-driving-the-order-matters\">What happens while driving - the order matters<\/a><\/li>\n<li><a href=\"#the-angle-matters\">The angle matters<\/a><\/li>\n<li><a href=\"#pre-drilling-and-the-thread\">Pre-drilling and the thread<\/a><\/li>\n<li><a href=\"#values-for-calculation\">Values for calculation<\/a><\/li>\n<li><a href=\"#the-product\">The product<\/a><\/li>\n<li><a href=\"#in-short\">In short<\/a><\/li>\n<\/ol>\n<\/nav>\n<p><!--fws-spis-wyglad--><\/p>\n<style class=\"fws-spis-wyglad\">\n.fws-spis{--s-paper:#FBFAF7;--s-bone:#F0EDE7;--s-ink:#14161A;--s-tekst:#4a4d52;\n  --s-cichy:#6E675F;--s-ramka:#e2ddd3;--s-linia:#ece7dd;--s-akcent:#E2541C;\n  margin:1.6rem 0 2.2rem;border:1px solid var(--s-ramka);border-radius:4px;\n  background:var(--s-paper);overflow:hidden}\n.fws-spis-tytul{margin:0;padding:12px 16px;background:var(--s-bone);\n  border-bottom:1px solid var(--s-ramka);\n  font:600 .72rem\/1.3 \"IBM Plex Mono\",ui-monospace,monospace;\n  letter-spacing:.12em;text-transform:uppercase;color:var(--s-cichy)}\n.fws-spis ol{margin:0;padding:0;list-style:none;counter-reset:fws-s}\n@media(min-width:760px){\n  .fws-spis ol{display:grid;grid-template-columns:1fr 1fr}\n  .fws-spis li:nth-child(odd){border-right:1px solid var(--s-linia)}\n}\n.fws-spis li{counter-increment:fws-s;margin:0;border-bottom:1px solid var(--s-linia)}\n.fws-spis a{display:block;padding:11px 16px 11px 40px;position:relative;\n  font-size:14px;line-height:1.45;color:var(--s-tekst);text-decoration:none;\n  transition:background .12s,color .12s}\n.fws-spis a::before{content:counter(fws-s,decimal-leading-zero);position:absolute;\n  left:16px;top:12px;font:400 11px\/1 \"IBM Plex Mono\",ui-monospace,monospace;\n  color:var(--s-cichy);font-variant-numeric:tabular-nums}\n.fws-spis a:hover{background:var(--s-bone);color:var(--s-ink);\n  box-shadow:inset 3px 0 0 var(--s-akcent)}\n.fws-spis a:focus-visible{outline:2px solid var(--s-akcent);outline-offset:-2px}\n.entry-content h2[id]{scroll-margin-top:96px}\n@media(prefers-reduced-motion:reduce){.fws-spis a{transition:none}}\n<\/style>\n<p><!--\/fws-spis-wyglad--><\/p>\n<h2 id=\"the-difference-is-mechanical-not-marketing\">The difference is mechanical, not marketing<\/h2>\n<p><strong>Partial thread<\/strong> has a smooth shank under the head. That section <em>does not grip the member being fixed<\/em> - it passes freely through it. As the thread pulls into the receiving member, the screw <strong>draws the two parts together<\/strong>. That is its job.<\/p>\n<p class=\"fws-ramka fws-ramka--uwaga\">This holds under one condition: <strong>the smooth shank must span the whole member being fixed<\/strong>. If the board is 40 mm and the smooth part only 30 mm, the thread starts to bite in the upper member, no clamping arises and the gap stays. It is the most common cause of &#8220;I used a partial thread and it still did not close&#8221;.<\/p>\n<p>For the same reason a full-thread screw <em>can<\/em> draw parts together if a <strong>clearance hole<\/strong> larger than the thread is drilled in the upper member. The thread then has nothing to grip on the way through and behaves like a partial one.<\/p>\n<p><strong>Full thread<\/strong> grips both members at once. It draws nothing together; it <strong>transfers force along the whole shank<\/strong>. Once it bites, the parts stay where they were.<\/p>\n<h2 id=\"where-the-weak-link-sits\">Where the weak link sits<\/h2>\n<p>With a partial thread, capacity is usually governed not by the thread but by the <strong>head pull-through resistance in the member being fixed<\/strong>. The head holds the upper part, and the material beneath it has limited bearing strength. The manufacturer states it directly: with a partial thread, <em>the significantly lower resistance of head penetration limits the strength of the connection in the fixed member<\/em>.<\/p>\n<p>With a full thread the head is not the weak link, because it is not carrying the load. Force spreads along the thread turns in both members.<\/p>\n<p>A practical rule follows: if the design quotes a <em>withdrawal<\/em> capacity, what counts alongside the diameter is the penetration depth of the thread in the receiving member, the timber density and the driving angle. If it quotes <em>head pull-through<\/em>, it is describing a clamping connection - and a partial thread belongs there.<\/p>\n<h2 id=\"the-third-variant-dual-zone-thread\">The third variant: dual-zone thread<\/h2>\n<p>Beside the two classic solutions there are screws with <strong>two thread zones<\/strong> - under the head and at the tip. They are easily mistaken for a full thread, and even more easily for each other, because a similar description covers two designs with opposite effects.<\/p>\n<p><strong>Pulling together by different pitch.<\/strong> If the two zones have different pitches, they advance at different speeds while driving, and that difference pulls the parts together. This is a solution for clamping two timber members - where the joint must be tight and the force has to run along the shank rather than through the head alone.<\/p>\n<p><strong>Holding the gap in above-rafter insulation.<\/strong> A double-threaded insulation screw such as Topduo does the opposite. The thread at the tip grips the rafter and the thread under the head grips the counter-batten, so the counter-batten stays at its distance and the insulation between them is <em>not compressed<\/em>. In a technical article the manufacturer states plainly that compression of the insulation can be prevented by using double-threaded screws - which is why Topduo suits both pressure-resistant and non-pressure-resistant insulation. Choosing the length is covered in our <a href=\"https:\/\/fixwoodsystem.pl\/en\/guides\/length-above-rafter-insulation\/\">guide to above-rafter insulation<\/a>.<\/p>\n<p>If a product description shows two thread zones, check the data sheet for which of these jobs the screw does: pulling together or holding the gap. Neither is the job of an ordinary full-thread screw.<\/p>\n<h2 id=\"how-to-choose\">How to choose<\/h2>\n<table>\n<tr>\n<th>Situation<\/th>\n<th>Thread<\/th>\n<\/tr>\n<tr>\n<td>The member must be <strong>clamped<\/strong> to the substrate - closing a gap, gluing, board fixing<\/td>\n<td>partial<\/td>\n<\/tr>\n<tr>\n<td>Reinforcement across the grain<\/td>\n<td>full<\/td>\n<\/tr>\n<tr>\n<td>Reinforcing a beam in shear<\/td>\n<td>full<\/td>\n<\/tr>\n<tr>\n<td>Rafter-to-purlin joints, braces<\/td>\n<td>full or partial - depending on geometry and loads<\/td>\n<\/tr>\n<tr>\n<td>Renovating a timber-beam floor<\/td>\n<td>full<\/td>\n<\/tr>\n<tr>\n<td>Fixing boards and sheathing<\/td>\n<td>depends on the head, not the thread<\/td>\n<\/tr>\n<\/table>\n<p>The manufacturer&#8217;s worked examples also calculate the rafter-to-purlin joint with a partial-thread screw (Paneltwistec) - the choice follows from calculation, not from a table.<\/p>\n<h2 id=\"why-full-stronger-is-a-bad-shortcut\" class=\"fws-znak fws-znak--wazne\">Why &#8220;full = stronger&#8221; is a bad shortcut<\/h2>\n<p>Full thread gets marketed as the better one because it sounds like &#8220;more thread&#8221;. That misleads in two ways.<\/p>\n<p>First, <strong>in a clamping job a full thread is worse<\/strong> - it cannot do the work being asked of it. Second, <strong>capacity depends on penetration<\/strong>, not on the total number of turns: what counts is the thread length in the receiving member. A full-thread screw driven too shallow has lower withdrawal capacity than a partial-thread one at the right depth.<\/p>\n<h2 id=\"the-common-mistake-and-what-it-looks-like\">The common mistake and what it looks like<\/h2>\n<p>A full-thread screw used where a gap needs closing <strong>will not close it<\/strong>. It locks the parts in the position it found them. If two millimetres of play remained between the beams, they are still there after driving - and the joint looks finished.<\/p>\n<p>Conversely, a partial thread in a cross-grain reinforcement delivers the capacity set by the head rather than by the thread - considerably lower than the design assumed. That is an invisible defect: the structure stands, but the margin the designer counted on does not exist.<\/p>\n<h2 id=\"cross-grain-reinforcement-where-it-really-shows\" class=\"fws-znak fws-znak--wazne\">Cross-grain reinforcement - where it really shows<\/h2>\n<p>Timber is much weaker across the grain than along it, and in tension the difference runs to a factor of several dozen: for C24, EN 338 gives a characteristic tensile strength of 14.5 N\/mm\u00b2 parallel and 0.4 N\/mm\u00b2 perpendicular to the grain. That is why cracks in beams run along the grain, and why reinforcement has to <strong>stitch them across<\/strong>.<\/p>\n<p>A full-thread screw acts here like reinforcement: it grips on both sides of the crack and carries tension through a plane that carries nothing by itself. A partial thread in that role only presses the edges together - and clamping does not replace reinforcement once the load pulls them apart again.<\/p>\n<p>This is the typical application in floor repairs and rafter strengthening, and the most common reason to reach for a full-thread screw at all. Where a crack is already visible, position matters too: the screw must cross the crack plane, not run within it - one set parallel to the crack holds only one side and achieves nothing.<\/p>\n<h2 id=\"what-happens-while-driving-the-order-matters\">What happens while driving - the order matters<\/h2>\n<ol>\n<li><strong>The tip cuts in<\/strong> and the screw starts to draw itself. There is no clamping yet.<\/li>\n<li><strong>The thread bites in the receiving member.<\/strong> With a partial thread the smooth shank slides freely in the upper part, so that part can still move.<\/li>\n<li><strong>The head reaches the surface.<\/strong> Only now does clamping arise, and it is what closes the gap.<\/li>\n<li><strong>Tightening.<\/strong> Once the head seats, further rotation <strong>keeps increasing<\/strong> the clamping force - right up to the point where the head embeds in the timber, the thread strips or the screw yields. So set a torque on the driver rather than tightening &#8220;until it stops&#8221;: nothing announces the limit except exceeding it.<\/li>\n<\/ol>\n<p>With a full thread, step three does not play that role - the head seats, but the parts are already bound by the thread and nothing will move closer. So the <strong>gap must be closed before driving<\/strong>, with a clamp or a wedge.<\/p>\n<h2 id=\"the-angle-matters\">The angle matters<\/h2>\n<p>In shear connections, full-thread screws are often driven <strong>at an angle<\/strong> rather than perpendicular. Set at an angle, the screw works mainly in <em>tension<\/em> rather than bending - and in tension it is considerably stronger.<\/p>\n<p>Angle, spacing and the number of fasteners follow the calculation, not a feel for it or experience from the last site. That is also why an approval quotes several different capacity values for the same screw.<\/p>\n<h2 id=\"pre-drilling-and-the-thread\">Pre-drilling and the thread<\/h2>\n<p>With larger-diameter structural screws, pre-drilling is needed for a different reason than with decking screws - it is not about shearing the head but about <strong>splitting the member<\/strong>.<\/p>\n<p>A screw entering timber pushes the fibres aside. Near an edge or the end grain that force has nowhere to go and the wood splits along the grain. The larger the diameter and the harder the species, the smaller the margin. The manufacturer specifies tips with <em>reduced driving torque and limited splitting effect<\/em> for structural screws, but that lowers the risk rather than removing it. Minimum distances come from the approval, and the approval <strong>distinguishes between tips<\/strong>. For exclusively axially loaded screws without pre-drilling, in members at least 10\u00b7d thick and at least 8\u00b7d or 60 mm wide (whichever is greater), ETA-11\/0024 gives a distance to the end grain a1,c = 10\u00b7d and to the edge a2,c = 4\u00b7d. For screws with a type BS or rBS DAG tip these drop to 5\u00b7d and 3\u00b7d. Which tip your screw has is in its data sheet - and it is the approval, not feel, that says how close to the edge you may go.<\/p>\n<h2 id=\"values-for-calculation\">Values for calculation<\/h2>\n<p>Characteristic capacities, minimum spacings and edge distances are in approval <strong>ETA-11\/0024<\/strong> and in the parameter sheet - both downloadable from the product page, without an account. We do not copy them here because they depend on diameter, species, penetration depth and driving angle. When an approval is needed and when it is not is covered in the <a href=\"https:\/\/fixwoodsystem.pl\/en\/guides\/eta-when-needed\/\">guide to ETA<\/a>.<\/p>\n<h2 id=\"the-product\">The product<\/h2>\n<p><a href=\"https:\/\/fixwoodsystem.pl\/en\/product\/konstrux-full-thread-cylinder-head\/\">KonstruX full thread, cylinder head<\/a> - galvanised steel, blue zinc coating, approval <strong>ETA-11\/0024<\/strong>. In our range, <strong>30 variants<\/strong>: diameters 5.2 \/ 5.9 \/ 6.5 \/ 8.0 mm, lengths <strong>80-330 mm<\/strong>.<\/p>\n<p class=\"fws-ramka fws-ramka--uwaga\">The manufacturer carries this family across a wider diameter range than we do. If you need a size outside that list, <a href=\"https:\/\/fixwoodsystem.pl\/en\/contact\/\">write to us<\/a> - we will check availability rather than offer you the nearest size.<\/p>\n<p class=\"fws-ramka fws-ramka--stop\">Note that KonstruX is <strong>galvanised<\/strong>. For tannin-bearing timber - oak, larch, chestnut - <a href=\"https:\/\/fixwoodsystem.pl\/en\/guides\/oak-larch-and-zinc\/\">galvanising is not suitable<\/a>, however well the screw performs structurally.<\/p>\n<h2 id=\"in-short\">In short<\/h2>\n<p>A partial thread <strong>draws together<\/strong>; a full thread <strong>stitches<\/strong>. You choose by the job, not by which sounds stronger. In a clamping job the full thread is worse, and in a cross-grain reinforcement the partial thread delivers the capacity set by the head - far less than the designer calculated. The numbers live in the approval, not the catalogue. And remember the material: the best thread in zinc still does not suit oak.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Full thread transfers force in both members, partial thread clamps them together. Which one when, and the mistake that costs most.<\/p>\n","protected":false},"author":0,"featured_media":1927,"parent":854,"menu_order":10,"comment_status":"closed","ping_status":"closed","template":"template-guide.php","meta":{"_acf_changed":false,"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"class_list":["post-855","page","type-page","status-publish","has-post-thumbnail","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/fixwoodsystem.pl\/en\/wp-json\/wp\/v2\/pages\/855","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fixwoodsystem.pl\/en\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/fixwoodsystem.pl\/en\/wp-json\/wp\/v2\/types\/page"}],"replies":[{"embeddable":true,"href":"https:\/\/fixwoodsystem.pl\/en\/wp-json\/wp\/v2\/comments?post=855"}],"version-history":[{"count":5,"href":"https:\/\/fixwoodsystem.pl\/en\/wp-json\/wp\/v2\/pages\/855\/revisions"}],"predecessor-version":[{"id":2308,"href":"https:\/\/fixwoodsystem.pl\/en\/wp-json\/wp\/v2\/pages\/855\/revisions\/2308"}],"up":[{"embeddable":true,"href":"https:\/\/fixwoodsystem.pl\/en\/wp-json\/wp\/v2\/pages\/854"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/fixwoodsystem.pl\/en\/wp-json\/wp\/v2\/media\/1927"}],"wp:attachment":[{"href":"https:\/\/fixwoodsystem.pl\/en\/wp-json\/wp\/v2\/media?parent=855"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}