Bolt Preload and Torque: Getting the K-Factor Right
Torque sets bolt preload through friction. Learn the T = K D F equation, how to choose the nut factor K, and a worked example on a Grade 8 bolt.
Threaded Joints
Threaded joints are probably the most common form of mechanical assembly. They allow for the inexpensive but effective joining of parts. This allows for less expensive manufacturing and easier maintenance, repair or servicing of a finished assembly.
To take advantage of threaded joints, you need to understand was standard sizes of threads exist, what types of bolts and hardware exist and what are the implications of different grades of hardware – in terms of size, mechanical properties, corrosion resistance and fastening strength.
Unified Screw Threads – Fine (UNF)
Unified Screw Threads – Course (UNC)
National Pipe Thread (NPT)
Metric Thread
ACME Thread
Socket Head Cap Screw (SHCS)
Hex Head Cap Screw (HHCS)
Button Head Cap Screw (BHCS)
Bolt Preload and Torque: How to Calculate Clamp Force
Turn torque into clamp force with T = K.D.F. Nut factor, 75% proof-load target, and a 1/2-13 Grade 5 worked example showing why lubrication changes everything.
Bolt Torque vs. Preload: Getting the Clamp Load You Actually Designed For
Torque is not clamp load — it is a proxy for it. This worked example shows how to calculate bolt preload and the correct torque using the T = K·F·d relation, for both a 1/2-13 Grade 5 and an M12 8.8 fastener.
Bolt Torque vs. Preload: Using T = K·D·F Without Guessing
Understand the bolt torque equation T = K·D·F, why the nut factor K drives accuracy, and how lubrication changes your torque spec — with a worked Grade 5 example.
Bolt Strength Chart — SAE Grade 2/5/8, ASTM A325/A490 & Metric Class 8.8/10.9/12.9
Imperial Bolt Strength Chart (SAE & ASTM) Standard strength ratings for carbon and alloy steel bolts up to 1″ diameter. These are the grades you’ll encounter on 99% of US engineering drawings. Grade Head Marking Material Proof (psi) Yield (psi) Tensile (psi) SAE Grade 2 No markings Low carbon steel 55,000 57,000 74,000 SAE Grade … Read more
Cutting Taps vs. Form Taps — When to Use Each and Why Drill Size Matters
What’s the Difference? Cutting taps and form taps both create internal threads, but they do it in completely different ways — and they require different drill sizes. Confusing the two is one of the most common (and costly) mistakes on a shop floor. Cutting Taps (Chip-Producing) Cutting taps work exactly like you’d expect: they have … Read more
Thread Engagement Length — How Many Threads Do You Need to Prevent Stripping?
Minimum Thread Engagement How deep does a bolt need to thread into a part before the threads strip? This is one of the most common questions in fastener design — and the answer depends on the relative strength of the bolt and the tapped material. Rule of Thumb Tapped Material Minimum Engagement Recommended Engagement Steel … Read more
Fastener Preload & Torque — How to Calculate Required Clamp Load
Understanding Bolt Preload Bolt preload is the tension (clamping force) induced in a bolt when it’s tightened. This preload is what holds your joint together — not the bolt’s ultimate tensile strength. A properly preloaded joint resists external loads by maintaining clamping force on the parts, preventing slippage and fatigue. Why Preload Matters More Than … Read more
Set Screw Torque Chart — Cup Point, Cone Point & Flat Point Holding Power
Set Screw Holding Power & Tightening Torque Set screws hold collars, pulleys, gears, and knobs on shafts. Their holding power depends on the point style, material hardness, and seating torque. Under-torqued set screws are the most common cause of components slipping on shafts. Recommended Tightening Torque Set Screw Size Cup Point Torque (in-lbs) Axial Holding … Read more
Clearance Hole Chart — Close, Normal & Loose Fit for US and Metric Bolts
Bolt Clearance Hole Sizes When a bolt passes through a part without threading into it, the hole needs to be slightly larger than the bolt diameter. How much larger depends on how precisely the holes need to align. US Bolt Clearance Holes Bolt Size Close Fit (in) Normal Fit (in) Loose Fit (in) #4 (0.112) … Read more