These are a "must use". You don't realize how much dirt gets into your light sockets which cause premature failures. These protective seals are very soft and pliable and easily installed on your sockets. Some bulbs require more than normal pressure to fully seat but all will work.
Purchased more rubber O-rings because they did a great job of keeping the snow out of the sockets which would cause them to crack and break without them.
These little O-rings are a nice finishing touch for your cords. They are easy to work with and provide a satisfyingly snug wrapper around the base of the lamp. If ordering large lots order a bit more than needed just in case a bag or two is a bit short of pieces.