The image below can help guide you to the correct part number you need if you are not familiar with the terms used to reference the undercarriage parts. Many people refer to them as wheels and pulley but in the industry there are several uncommon terms for the rollers, and idlers. Place your mouse over the image below and the drive sprocket, rubber track, front idler, bottom track rollers and rear idler will pop up with the correct term and link for you to learn more. Don't hesitate to call with any questions you have. Each manufacturer has different terms for these parts. The picture below is from the Caterpillar® 299c series machine. These parts fit on the 279c and 289c as well but some require only four bottom rollers.