PAP bush PCM1820-20E-SKF

What do suffixes mean ...?
P10, P20, P11 and P14 ? 
This is the type of coating applied on this smooth ring: 
P10 = self-lubricated PTFE (Teflon) coating, will not require maintenance 
P20 = PTFE (Teflon) self-lubricated honeycomb coating, with a grease hole, which will allow maintenance and lubrication of the ring 
P11 = self lubricated PTFE (Teflon) coating, which will not require maintenance. High thermal and antimagnetic conductivity 
P14 = Self lubricated PTFE (Teflon) coating, which will not require maintenance. Does not contain lead and is therefore a more ecological product. 
What is the purpose of a smooth ring? 
 A smooth  ring  has a similar use to bronze  rings , in generally smaller thicknesses than the  ring  bronze. > It will serve as a guide in rotation of an axis with respect to a fixed reference, where a minimum size is necessary. 
The wear on the bushings is slow and takes up little time. 
Some versions are maintenance-free, and can run dry.   Operating temperature ranges are very wide: -200 ° C to + 280 ° C.