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	Mild steel	Dry and clean	$0.61$	$0.47$	$0.55$	$31$	$0.44$	$25$
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	Concrete	Dry and clean	$0.62$	?	$0.55$	$32$	?	?
Wood	Metal	Dry and clean	$0.2-0.6$	?	$0.2-0.54$	$11.3-31$	?	?
Wood	Metal	Wet	$0.2$	?	$0.2$	$11.3$
Wood	Wood	Dry and clean	$0.25-0.5$	?	$0.24-0.46$	$14-26$	?	?
Wood	Wood	Wet	$0.2$	?	$0.2$	$11$	?	?
Mild steel	Mild steel	Dry and clean	$0.74$	$0.57$	$0.64$	$37$	$0.52$	$30$
Hard steel	Hard steel	Dry and clean	$0.78$	$0.42$	$0.66$	$38$	$0.40$	$23$

For more, see The Engineer's Handbook and Engineering Toolbox.