Oar leathers go between the oar and the oarlock.  If you row a boat much, the oars will get chewed up without them.  

I took a suggestion from Dynamite Payson in one of his instant boat books and used braided nylon line in place of leathers.  Basically, you wrap the line (I used 1/8") around the oar and hold it in place with brass brads.  It's worked fairly well, although I should have wrapped the line tighter.  The price was certainly right!

Steve Tyree, P-15