Screw/Nut and Thrust-Collar Friction Coefficients
Friction coefficients f for screw/nut material pairs (steel, bronze, brass, cast iron; dry and machine-oil) and thrust-collar friction fc running/starting for steel-on-cast-iron and steel-on-bronze — power-screw friction reference tables.
Last updated: 2026-11
Specifications
Power screws — the threaded shafts that turn rotation into linear force in presses, jacks, valve stems and linear actuators — live or die by two friction numbers, and the collected tables carry both. Table 1 is the screw/nut pair friction f: steel-on-steel 0.15-0.25 dry (0.11-0.17 with machine oil), steel-on-bronze 0.15-0.23 dry (0.10-0.16 oiled), bronze-on-bronze 0.04-0.06 (the low point of the table — with a "-" where bronze-on-brass is not tabulated), steel-on-cast-iron 0.15-0.25. Table 2 is the thrust-collar friction fc where the rotating member bears its axial load: soft steel on cast iron 0.12 running/0.17 starting, hard steel on cast iron 0.09/0.15, soft steel on bronze 0.08/0.10, hard steel on bronze 0.06/0.08 — starting friction running 30-60% above running, the margin every drive sizing must carry. Sources are Shigley's Mechanical Engineering Design and the Mechanical Design and Systems Handbook, as the tables' own closing rows print.
| Table 1 — screw/nut f | Steel/steel 0.15-0.25 dry, 0.11-0.17 machine oil; steel/bronze 0.15-0.23 dry, 0.10-0.16 oiled; steel/brass 0.15-0.19 dry, 0.10-0.15 oiled; steel/cast iron 0.15-0.25 dry, 0.11-0.17 oiled; bronze/steel 0.08-0.12; bronze/bronze 0.04-0.06 (brass column "-"); bronze/cast iron 0.06-0.09 |
|---|---|
| Table 2 — collar fc | Soft steel/cast iron 0.12 running, 0.17 starting; hard steel/cast iron 0.09/0.15; soft steel/bronze 0.08/0.10; hard steel/bronze 0.06/0.08 |
| Sources (as printed) | Shigley's Mechanical Engineering Design and Mechanical Design and Systems Handbook — carried verbatim as the tables' closing rows |
| Not tabulated | Thread-form efficiency (Acme/trapezoidal geometry factors), wear rates, PV limits for the nut material — per RFQ / design text |
Materials
- The bronze nut exists for a reason: bronze-on-steel halves friction, resists seizure against the steel screw and wears sacrificially — it is the default nut material for power screws above toy scale, with the collar numbers showing the same bronze advantage at the thrust face. Specify the pair, not just the screw: a steel nut substitution on a bronze-specified jack changes both the efficiency and the wear life. Lubrication state is the second axis — the dry-to-oiled spread in table 1 is a third of the friction, and power screws are usually the last place anyone remembers to oil
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (Screw/Nut and Thrust-Collar Friction Coefficients) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
How do these two tables combine in a power-screw torque calculation?
The total torque to raise a load sums two terms: thread friction (from table 1's f, through the screw geometry) and collar friction (from table 2's fc, at the thrust face radius). Each carries its own coefficient, which is why the two tables are separate — a bronze nut on a steel screw with a hard-steel-on-bronze collar uses f ≈ 0.10-0.16 at the threads and fc ≈ 0.06-0.08 at the collar, and starting conditions use the higher fc column for the breakaway torque. Sizing a motor or hand-wheel off running friction alone is the classic under-specification: the starting column is 30-60% higher, and the drive must start.
Why is bronze-on-bronze marked "-" for the brass column, and what pair should I actually choose?
The "-" is the source's marker that the bronze-screw/brass-nut combination is not tabulated — combinations like that are rarely used and the handbooks leave them out rather than estimate. The practical selection ladder the tables do support: bronze nut against a steel screw for general power screws (moderate friction, seizure-resistant, wear taken by the replaceable nut); cast-iron nut where loads are light and cost rules; steel nuts only for light-duty positioning where friction and galling risk are acceptable. Whichever pair, quote both members on the RFQ — nut material is a designed choice, and the friction tables are its justification.
Related knowledge
- Thread-Forming vs Thread-Cutting vs Thread-Rolling Self-Tapping Screws: What the Evidence Settles on Base Material
- Screw Family Selection by Base Material: Wood, Machine and Self-Tapping Threads, Engagement and Coating
- Hex Bolts vs Socket Head Cap Screws: What the Evidence Settles on Strength, Clearance and Cost
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What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
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- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
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