Table of friction coefficients

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

For more, see The Engineer's Handbook