Coefficient of Friction

Approximate coefficients of friction for common material pairs. Static (µs) is the force to start sliding; kinetic (µk) to keep sliding. Real values vary widely with finish, contamination and load.

Material pair	Static µs	Kinetic µk
Steel – steel (dry)	0.60	0.42
Steel – steel (lubricated)	0.10	0.05
Steel – cast iron	0.40	0.23
Steel – brass	0.51	0.44
Aluminium – steel	0.61	0.47
Copper – steel	0.53	0.36
Steel – PTFE (Teflon)	0.05	0.04
Nylon – steel	0.40	0.30
Brake lining – cast iron	0.40	0.30
Rubber – dry asphalt	0.90	0.65
Wood – wood	0.40	0.30
Glass – glass	0.94	0.40
Ice – ice	0.10	0.03

Use in the capstan, lead-screw and snap-fit tools.

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