During much of production (i.e. in Tunisia as seen in the top photo in Scarf's post), 2 washers.
After much abuse (including one documented drop to the ground in Tunisia), by the end of filming (i.e. as seen in screen caps of when the saber is dropped on Obi's cloak), 1 washer, as seen in the 2nd photo in Scarf's post, which is presumed to have been taken as documentation after filming.
There was possibly more than one prop as well, in which case there is no evidence of the 'Chronicles' saber (the one in the 2nd picture) as having ever had two washers. The saber in the first picture has some anomalies vs. the 'Chronicles' saber. Some argue that it may simply have been rebuilt after being damaged.