Polini Kelvar Belt for 50cc 4-Stroke 139QMB Scooters (Short Case)P 248.036 – Replaces the stock size belt 669-18-30 used in most 139QMB engines. However, some use the 788 size belt which replacement would be P 248.029, so please know your size when ordering. All it takes is looking at your stock belt to check size.Polini Kevlar Variator Belt. Low friction Polini variator belt, featuring aramid fibre inlay, making it extremely robust. It`s no coincidence that this belt is Polini`s first choice for the race track. Additional grip means that cold-slip is minimised. This belt is at home on the track, but is also a great upgrade for a standard engine that is being put through its paces. Dimensions: 683-18.2-30**NOTE: DELIVERY MAY TAKE UP TO 2-3 WEEKS****