These self-lubricating bushings contain graphite plugs which are 
impregnated with oil. When the bushing reach 80-90°F as a result of 
friction between the bushing and guide post, oil is drawn from the plug, 
thus lubricating the wear surface. A dark smear pattern is created on 
the wear surface as the oil and graphite are imbedded into the bronze 
or steel grain. This provides the lubrication necessary for continuous 
performance of the tool.