[Specification] Open [Advantage/Disadvantage] No friction Easy to re-lube No protection against contamination [Design] 
No seals
N o s e a l s
M e t a l s h i e l d s
R u b b e r s e a l
P T F E s e a l s
P T F E s e a l s w i t h m e t a l s h i e l d s
V i t o n s e a l s