Technical Library
Common problems in fastener design and procurement, addressed from the perspective of a manufacturer with over 50 years in the trade.
Tightening torque and preload calculator — allowable torque, set torque, preload range
Enter size, property class, head type, friction range and torque scatter to get the maximum allowable torque, the set torque with its scatter band, and the preload range. Simplified VDI 2230.
Most tightening torque goes into friction — why preload differs at the same torque
Why a bolt tightened to the specified torque can still break or work loose. Where the torque goes, and how much preload changes with friction, with a worked example and graph.
What pilot hole for a tapping screw? — the hole sizes in KS are test conditions
When a tapping screw strips, the pilot hole is the first thing to check. What the hole diameters in KS B 0251 mean, what happens when the hole is too small or too large, and the caution for stainless tapping screws.
My Stainless Bolt Seized Halfway In — Galling
A common failure in stainless fastening. Causes and practical ways to reduce the risk.
Reading a Screw Designation — What M4 × 0.7 × 10 Means
Breaking down the fastener callout on a purchase order or drawing, item by item.
Tightening, Loosening and Breaking Torque
The three torque values, what the standard's minimum breaking torque means, and how to set the right tightening torque.
How deep should a bolt engage? Thread engagement length and tap depth
Reference engagement lengths by base material, effective engagement and load sharing, and how to set blind-hole drill depth.
Phillips bit size chart — numbers differ between KS and ISO
The same M3 can take a different recess number depending on the standard. KS vs ISO chart, PH vs PZ, why recesses strip and how to choose a bit.
Tapping screws type 1 and 2, and trilobular thread-forming screws — point, use and how to choose
Sharp point is type 1, blunt point is type 2, and a rounded-triangle cross-section is a trilobular thread-forming screw (often called TAPTITE). Choose by base material and pilot hole, then confirm with a trial.
Seven screw head types — pan, truss, binding, countersunk: which to use when
Choose a head by bearing area, protrusion and whether a countersink is possible. Even at M4, head diameter ranges from 6.0 to 9.4 mm.
SEMS screws (screw and washer assemblies) — spring and plain washer combinations
A screw with the washer fitted before the thread is rolled, so it cannot fall off. Choose spring washer only or spring plus plain washer, and standard or large plain washer.
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