Table of friction coefficients

First surface	Second surface	Condition	${\mu }_s$	${\mu }_k$	${\tan }^{-1}({\mu }_s)$ (radians)	${\tan }^{-1}{\mu }_s)$ (degrees)	${\tan }^{-1}({\mu }_k)$ (radians)	${\tan }^{-1}({\mu }_k)$ (degrees)
Aluminimum	Steel	Dry and clean	$0.61$	$0.47$	$0.55$	$31$	$0.44$	$25$ degrees
Aluminimum	Aluminimum	Dry and clean	$1.05-1.35$	$1.4$	$0.81-0.93$	$46-53$	$0.95$	$54$
Copper	Steel	Dry and clean	$0.53$	$0.36$	$0.49$	$28$	$0.35$	$20$ =
Copper	Copper	Dry and clean	$1.0$	?	$0.79$	$45$	?	?
Wood	Wood	Dry and clean	$0.25-0.5$	?	$0.24-0.46$	$14-26$
Wood	Wood	Wet	$0.2$	?	$0.2$	$11$	?	?

For more, see The Engineer's Handbook