The nylon friction pad is inserted in the hole in the end of the window operator. It slides in a channel on the front aluminum frame of many Hehr windows from the 1950s and 1960s.
It is 1-1/2" long and 1/4" wide. It is installed by folding the friction pad then inserting the round ends together through the hole in the arm, this forms a loop in the nylon part. This nylon loop slides in the aluminum channel when opening and closing the window. There is a very tiny spring which goes between the nylon pieces to put good pressure on them. Be very careful when removing old friction pads that you do not loose the spring because they are no longer available.
Sold each and spring is not included.