There is often some confusion when people go to buy a replacement oil skimmer belt. There is a tag on the side of the skimmer for the specific belt part number, but this will wear off from time to time. The first things you need to look at are the type of skimmer and what the belt material looks like. The more complicated part comes in when figuring out what length of belt is needed. Some units will measure the reach from skimmer mounting down, while other skimmers will measure from center of the top pulley to center of the bottom pulley. The most frequent mistake made is measuring the belt when it is folded over or measuring the full circumfrence. The best way to ensure that you are getting the correct oil skimmer belt is to ask your sales representative.